Employee Voice: The Missing Factor in Sustainable HRM?

: Sustainable Human Resource Management (HRM), has the potential to facilitate organisations development of principles, policies and practices for the challenges of the 21st century. However, to do this we argue a fundamental element in this process has yet to be fully addressed and incorporated into the theory and practice of sustainable HRM; this is employee voice. Additionally, the actual and potential role of trade unions in facilitating employee voice is yet to be conceptualised within sustainable HRM literature. We argue that the development of effective employee voice mechanisms is vital in the implementation and maintenance of sustainable HRM. In this conceptual paper, we outline the nature of the voice architecture, the impact of the employment relationship on voice mechanisms, how it can be effectively measured, and propose a framework for further exploring these concepts. These key factors we identify as critical in implementing and assessing the effectiveness of the relationship between employee voice and sustainable HRM, to potentially serve as a basis of future research into sustainable HRM.


Introduction
As economies across the world grapple with responding to the twin crises of a global pandemic and climate change, organisations too are finding ways to adapt to the myriad of changes and challenges both crises present. Within this context, there have been numerous calls for Governments and businesses to "build back better" [1]; that is, encouragement towards the economic recovery from the ramifications of the COVID-19 global pandemic to be based within sustainability objectives, thus responding to both crises concurrently. Such an approach encourages organisations to move beyond an emphasis on economic goals and outcomes, and to broaden their focus to include environmental and social goals and outcomes. Sustainable Human Resource Management (HRM) is an emerging field that provides a way for HRM to support an organisation's movement towards a broader focus and longer-term view [2]. Sustainable HRM expands HRM's remit beyond the traditional focus on economic goals, to a "triple bottom line" viewpoint, whereby environmental and social goals, in the short and long term, become an articulated aspect of HRM's role [3,4]. A central aspect of "building back better" is focused on a worker-centric approach [5][6][7]. As such, sustainable HRM has the potential to develop alongside government and organisation drives to "build back better", through seeing the critical role of the management of human resources in all aspects of both economic recovery and addressing the implications of climate change.
However, despite the central role human resources can play in achieving sustainability objectives, a fundamental element that we see as missing in Sustainable HRM literature is the role of the employee, and more specifically structured employee voice, in the development of a sustainable approach to HRM. Within the emergent literature on Sustainable HRM, there is research that brings the employee to the fore such as [8,9], including some that explore the impact of employee involvement or participation on environmental initiatives for example; [10][11][12][13]. Other work in the Sustainable HRM field has explored other aspects of HRM, such as recruitment and selection [14,15], training and development [16,17], Performance Management [18] and Reward Management [19] and its role in developing sustainability. Such research is often based on case studies or surveys on employee participation in environmental initiatives and focuses exclusively on the ecological aspect of Sustainable HRM, termed "Green HRM".
The role of the employee as a stakeholder in Sustainable HRM discussions to date has been largely overlooked in favour of more macro-level analysis [9]. This is despite employees' potential role as an influence on the uptake, development and ongoing support for sustainable HRM policies and practices. As such, this paper develops the conceptual argument that employees are key stakeholders in the formation and development of the organisations' human and social capital, and are a key source of knowledge and support for the development and implementation of Sustainable HRM.
The objective of this paper is to conceptually explore the critical role of employee voice in developing and maintaining communication channels to facilitate sustainable HRM within the workplace. Employee voice refers to the mechanisms through which employees attempt to have a say about aspects of their work, be it formal and/or informal channels, or individually and/or collectively [20]. We use the Employee Voice conceptual model of Cox, Zagelmeyer and Marchington [21], which highlights the need for the breadth (the linkage between voice channels) and depth (the degree of embeddedness) of involvement of practices like employee voice, and not just their presence or absence. This takes the focus to the issue of quality of voice rather than simply quantity, a point we argue is essential for the development of sustainable HRM to ensure it is not seen as a management fad. We will argue that such a bedrock approach to employee involvement is essential in the development, quality and maintenance of sustainable HRM. The structure of the paper is as follows. Firstly, we outline the development of sustainable HRM. Secondly, the paper explores the relationship between sustainability and employees, which leads to the analysis of the relationship between sustainable HRM and employee voice. From this, we explore the development of a model to analyse the quality of employee voice in relation to these new patterns and practices associated with sustainable HRM.

Sustainable HRM
The dominant paradigm in contemporary human resource management research both in practice and in theory over the last three decades has been Strategic HRM [22]. More recently, the focus of Strategic HRM on the financial outcomes of the organisation has begun to be questioned. Increasingly a more holistic approach is exploring the impact of HRM on outcomes besides the financial and economic aspects of the organisation [2,3,[23][24][25][26]. Sustainable HRM builds upon strategic HRM by acknowledging that HRM practices can, do, and arguably should, impact on economic measures and outcomes of the organisation, but importantly, sustainable HRM adds the social and environmental dimensions in which the organisation operates. As such, Kramer [3] explains that sustainable HRM literature can be seen as "an attempt to grapple with the relationship between HRM practices and outcomes beyond predominantly financial outcomes".
Defining Sustainable HRM has generated considerable debate, reflecting differing approaches and frameworks of understanding this concept. Drawing on The Brundtland Commission's [27] report, Kramer [3] defines sustainable HRM as "the patterns of planned or emerging HR strategies and practices intended to enable the achievement of financial, social and ecological goals, while simultaneously reproducing the HR base over a long term". Notable in this definition is the focus on The Brundtland Commission's [27] three pillars of sustainability; financial (or economic), social, and ecological (or "green"). Adopting these three pillars, Sustainable HRM can thus be seen as an extending beyond Strategic HRM definitions, which tend to focus on financial outcomes, and internal Corporate Social Responsibility (CSR), with its focus on social outcomes "towards the betterment of society" [28]. While the three pillars offer a useful representation of extending HRM's focus, there is some debate around the relative importance of each pillar. Enhert et al. [24] ques-tioned whether the three pillars should be considered as equally important, if economic needs take precedence, or if the three pillars can in fact be thought of as concentric circles, with the ecological dimension the outer circle.
The key issue, however, is the expansion of HRM's focus to explicitly include social and ecological dimensions in addition to the traditional focus on economics. In developing these concepts, Kramer's [3] definition of Sustainable HRM also incorporates a temporal dimension, highlighting that a sustainable approach to HRM meets both current and future needs of employees, organisation and society. As Wagner [4] argues, a sustainable HRM approach should be designed to "meet the current needs of a firm and society at large without compromising their ability to meet future needs". Ehnert [23] suggests it is this replicability of human resources over time that is an important driver towards a sustainable approach to HRM, stating that from this perspective, an organisation "sustains access to the desired groups of people and retains a healthy and productive workforce over time". The inference to an on-going relationship with the workforce is already clear. A more sustainable approach to HRM acknowledges the importance of looking into the longer term, ensuring the approaches taken by HRM help support the availability of suitable labour into the future (e.g., through being an employer of choice, placing high value on employee health and well-being, training and developing employees in preparation for future positions), as well as supporting the overall business to long term success (e.g., supporting staff to achieve business' economic, social and ecological goals, educating staff on environmental conservation efforts, creating policies to support staff contributing to social goals) [23,24].
The key gap in the literature to us is how these new networks, issues and information are enacted, communicated and supported throughout the organisation with the support of employees. This we see as a key conceptual shortcoming on the importance of employee voice currently in the literature, and an issue this paper will attempt to address.

The Employee and Sustainable HRM
Sustainable HRM literature that places the employee at the core of its full development and maintenance is limited as it tends to focus on one of the three pillars of sustainability, rather than a more holistic view of the employee within the sustainable HRM field. To elucidate, there is a small but growing body of work that has considered the employee within the ecological pillar of sustainable HRM, known as Green HRM (see for example [29]). There is also a well-established field of Corporate Social Responsibility (CSR) [30], which lends itself to the social pillar of sustainability [28]. The role and impact of and on the employee within the economic pillar of sustainability has been well traversed under the banner of Strategic HRM. As the economic aspect of sustainable HRM has been thoroughly covered for example [31][32][33][34], we focus on reviewing the research to date that has explored the employee within the ecological and social dimensions of sustainability.
Turning first to the ecological aspect of sustainability, Green HRM has been defined as "those parts of sustainable HR management dealing with the needs that relate to environmental sustainability. Green HR management is thus a subset of sustainable HR management where the latter also comprises corporate social responsibility (CSR) issues" [4]. Exploration focusing on Green HRM has been steadily growing over the past two decades. Paulet et al. [29] provide a meta-review of the Green HRM literature, articulating the main topics of focus within research and practice in the field.
Research into Green HRM at the employee level has found that employees are an important catalyst for an organisation to achieve its 'green' ambitions. Empirical research has demonstrated the impact employees can have on an organisation's environmental performance through employee's organizational citizenship behaviour towards the environment (OCBE) [8,[35][36][37][38], employee involvement in team projects [39][40][41], employee participation programs [11][12][13][42][43][44], or employee's abilities, motivations and opportunities (AMO) [9]. While the research finds that employees do affect environmental outcomes through Green HRM, a gap in the literature exists in the consideration of how employees can voice and be part of the drive towards and development of, environmental initiatives. An excep-tion is Markey et al. [10,45], who found that employee participation in reducing carbon emission strategies is important, and also that the nature of the employee participation schemes, in terms of quality and quantity, matters. Such a finding within the Green HRM domain of sustainability adds support to our argument that both the role, and the type, of employee voice mechanisms needs to be conceptualised within the growing sustainable HRM literature.
While Green HRM explores the ecological pillar of sustainability, some literature in the CSR field explores the social pillar. There is some overlap between the definitions of Sustainable HRM and Corporate Social Responsibility (CSR). Aguinis [46] defines CSR as "context-specific organisational actions and policies that take into account stakeholders' expectations and the triple bottom line of economic, social, and environmental performance". Gupta's [28] CSR definition focuses more on "the betterment of society". Whilst there are similarities to Kramar's [3] sustainable HRM definition used in this paper, the important difference lies in consideration to the temporal dimension; with sustainable HRM putting to the fore the replicability of resources into the future.
A sub-set of the CSR literature has focused on the employee within this 'social' pillar of the triple bottom line. Aguinis and Glavas' [30] meta review of CSR literature identifies conceptual papers that have considered employee perceptions of CSR see, e.g., [47]; individual employee discretion see, e.g., [48]; and the importance of CSR to employees see, e.g., [49]. Further research within CSR has explored the outcomes of CSR on employees in aspects, such as employee engagement, organisational citizenship behaviour, employee commitment and firm attractiveness [30].
Ybema, van Vuuren and van Dam's [50] research into sustainable employability, considered a subset of CSR [51,52], found that the effectiveness of HR practices aimed at increasing sustainable employability of employees was improved when more employees participated in the design of these practices. This is an important finding in indicating that under the social pillar of sustainability, employee voice has a role to play in designing and implementing policies directed towards sustainable HRM practices and a sustainable organisation more widely. This also means a role for a main arbiter of employee voicetrade unions.

Trade Unions and Sustainable HRM
As noted, an additional stakeholder to be considered when exploring Employee Voice in Sustainable HRM is the actual, and potential, role of trade unions (TU). Traditionally, TUs have played varying roles in employee voice mechanisms, ranging from strong, cohesive voice representation of employees, through to minimal to no role in representing employee interests, including voice [53]. Within these extremes, there is growing evidence of TUs playing a role in contributing towards sustainable HRM. Internationally, unions, supported by environmental advocacy groups (e.g., Greenpeace), are developing environmental policy that calls for a "just transition" towards a "net zero" emissions economy, e.g., see [54]. Just transition recognizes that environmental policies should be designed to ensure the costs and benefits of environmental transition are distributed fairly across society and between communities; and existing inequalities must not be worsened in the process of transition. This approach is not only more equitable, but it also arguably enhances the political credibility of change and ensures that social or political groups do not stand in opposition to a rapid shift towards a low-carbon economy.
Unions are seen to offer a key role in terms of collective worker voice and supporting sustainability through their traditional health and safety concerns in the workplace [55]. Motivations for engagement with sustainability in terms of environmental protection in the form of "just transition" and "green job" initiatives might include renewing union activity and "workplace greening" [56], creating stronger alliances between trade unions in traditional occupations and other "civil society" organisations [54] and, importantly, extending traditional workplace health-and-safety goals to include social and environmental sustainability. Britain's Trade Union Council (TUC) [57] advocate for a worker-centred just transition, arguing that: . . . there are no climate deniers in the trade union movement, but workers are much more enthusiastic about the drive to a 'net-zero' carbon economy if it is something done in partnership with them than if it is implemented by politicians and managers above their heads, with unions having no say in the process.
In the UK since 2006, trade unions have attempted to strengthen engagement in sustainability issues at sectoral and workplace level by calling for major investments in energy efficiency and renewable technologies [58,59], and bringing forward environmental issues into "mainstream" bargaining agendas through the "Green Workplaces" initiative [60]. Arguably, the TUC's Green Workplaces initiative falls within the issues-based partnership approach as it seeks to make the case that a union-management partnership on environmental issues will have "mutual gains" outcomes for workplace innovation, resource efficiency, and improved employment relations. This form of environmental bargaining has been identified as "a potentially important strategic mechanism for developing workplace-level responses to climate change" [45]. In the case of employer driven initiatives, unions may benefit from a "seat at the table" and a voice for workers in how best to design and implement these initiatives and may also help in overcoming potential employee resistance to environmentally friendly practices [61]. While there are examples of unions advocating for employee voice within transitions to net zero emissions economies, such as the British example above and "just transition" approaches in Germany and Canada [62], and in Australia [63], there is also evidence of how the transition to a low emissions economy is becoming a growing tension point for the labour movement in the USA [64]. While these examples demonstrate that unions have a role to play in environment initiatives, albeit supportive or non-supportive, the role of unions in this transition has received limited attention [65,66].

Employee Perspectives
As we have alluded to above, a paradox exists within the Sustainable HRM literature; while it is acknowledged that employee's perceptions and attitudes towards sustainability are influential in achieving sustainability objectives, little focus has been given to exploring what employee's sustainability perceptions and attitudes actually are. This paradox can be illuminated with a focus on the Green HRM sub-set of sustainable HRM. It has been found that "an individual's attitudes likely correspond to them refraining from green behaviours, or behaving in, green ways" [9], with a range of other research demonstrating the link between employee's sustainability attitudes and achievement of an organisation's sustainability objectives [8,37,44]. Blok et al. [67] found that "environmental awareness and personal norms have a significant impact on the intention to act pro-environmentally and therefore, have an indirect positive impact on PEB [pro-environmental behaviour] in the workplace". Despite the reported impact of employee attitudes on achievement of environmental goals, what employee's attitudes actually are towards environmental and sustainability goals has been overlooked in the research.
An additional concern emerging from the extant literature is a tendency for research to adopt a top-down perspective when exploring employees' roles in sustainability. Specifically, research tends to focus on how management behaviour and 'down-wards' communication can influence employee's sustainable behaviours in the workplace [68]. This is evident in a range of Green HRM research, such as how HR activities can be implemented to influence employee's sustainable behaviour [69,70] and how organisation's environmental actions impacted on employee's 'green' attitudes [44]. We suggest that such a top-down unidirectional approach is reflective of a lack of consideration of employee voice within the sustainable HRM literature to date. That is, consideration of the breadth and depth of employee voice mechanisms within sustainability research would facilitate a "two-way" perspective, allowing the opportunity for further understanding of the ways in which employee can and do shape sustainability objectives from the bottom-up. Such an approach would have "the potential to provide a platform for the continuous flow of information between management and employees on sustainable HR issues, policies and practices" [68].
We have three concerns with the extant literature's inattention to employee's attitudes towards sustainability. First, without knowledge and understanding of employee's sustainability attitudes, successfully motivating and engaging employees towards sustainable behaviour would potentially be negated. The research has found that employee support and engagement with sustainable behaviour is important to success in this area, but harnessing this potential drive towards sustainable goals, without initially understanding their employee's attitudes towards sustainability, creates difficulties in knowing where to direct efforts to best achieve sustainability goals. This is critical in the success of these new policies and principles as such an approach provides the foundation to build such practices. Second, as noted above, the research to date largely adopts a management top-down perspective when exploring sustainable HRM. We argue that an employee perspective to achieving sustainable HRM, through employee voice, can significantly contribute to an organisation achieving sustainability, both in their human resources and throughout the organisation. In order to fully understand the role of employee voice in sustainable HRM, we need to understand employee's attitudes and perceptions towards sustainability first, to know what the employee's "voice" may say on this topic. It is also critical we argue for an integration of the three pillars of sustainability; financial (or economic), social, and ecological (or "green"), but critically doing this in the context of current and future resources allocation. Finally, simply just having a voice mechanism is not enough, it is the quality of such processes that are likely to provide a solid bedrock for the development of work patterns and practices such as sustainable HRM both now and into the future, an aspect yet to be empirically evaluated. This bedrock we argue starts with trust.

The Escalator of Trust
A key element or foundation in the development of the escalator of participation is the level of trust in the relationship between management and employees and/or their representative. In understanding the dynamic nature of trust within the employment relationship and through employee voice, Korczynski [71], argues that trust is based upon the understanding of each parties' knowledge of the others vulnerabilities, but not exploiting them. In this way quality relationships can be built around the on-going employment relationship through the key communication channels of employee voice as Holland Cooper and Sheehan [72], have identified in their research.
Trust is therefore seen as the basis for quality relationships, cooperation and stability [73]. In understanding the dynamics and development of trust, a theory that has usefully captured this in the context of the employment relationship is Social Exchange theory (SET) [74]. From the SET perspective, the nature of the on-going employment relationship is to a large extent built on ambiguity, and this is increasingly seen as important with many arguing the contemporary concept of VUCA (Volatility, Uncertainty, Complexity and Ambiguity) best describes the pandemic and post-pandemic global environment of the early 2020s. In this context trusting relationship can build a certain level of stability and certainty in this environment [75]. This frame of reference also provides an opportunity to understand the development of employee voice identified along an escalator of participation, and as discussed below the potential to evaluate organisations movements both and up and down the framework as major issues and events emerge. It can also provide a reference point for both sides to reflect on and improve the nature of their voice system.

The Employment Relationship
As noted above, the contextual impact on Sustainability in the employment relationship is both critical and central to understanding how effective such policies and practices can be. Research commissioned by the CIPD [76] highlights that employee voice and dialogue between employers (management) and employees are seen as important elements of job quality and good work. They argue that "the ability to speak, be listened to and have an influence are valued in themselves" but are also critical to shaping and delivering other aspects of job quality and fair workplaces [76]. This is closely linked to the UN's Sustainable Development Goal (SDGs) 8 "decent work" and the need for "inclusive, participatory and representative decision-marking at all levels" in SDG target 16.7 [54]. Recent research by Lopez-Cabrales and Valle-Cabrera [77] explains how the nature of the employment relationship influences sustainability. Drawing on the work of Ehnert [23], they argue that "employment relationships are affected by sustainability in terms of their temporal orientation (short vs. long term), job security, career expectations, modifying the offers made by employers to employees as well as expected employee behaviours" [77]. They propose that "sustainable employment relationships" considers two dimensions: incentives offered by an organisation and expected employee behaviours to comply with sustainable HRM strategies.
To examine how the nature of the employment relationship influences sustainability outcomes, it is important to first outline three defining characteristics of the employment relationship emphasised by HRM and employment relations scholarship [77,78]. The first of these features is indeterminacy. The employment contract itself is necessarily indeterminate and the amount of work to be performed within the time period will be subject to debate and conflict. This indeterminacy of the employment relationship leads to different levels and forms of regulation within most national employment relations systems: as parties involved, employers, unions, and the state, seek to pursue their particular interests. The second defining aspect of the employment relationship is that it is unequal. The unequal employer-employee relationship is multifaceted and is shaped by a number of variables, particularly levels of unemployment, market competition, employee skills, and organizational resources such as trade unions and management philosophy. For example, in contrast to mainstream economics, employment relations scholarship assumes that labour markets are not perfectly competitive and thus employers typically have greater bargaining power than employees. The third defining feature of the nature of the employment relationship arises from the first two; it is dynamic in the sense that it is proceeds by the co-existence of both cooperation and conflict in varying degrees. While both employers and employees have a shared interest in the success of the organization, there exist at least some unavoidable, conflicts of interest between employers and employees (e.g., higher wages versus higher profit), which reflects the nature of capital and labour coming together. In other words, the employment relationship can be characterised by the existence of a "structured antagonism" [79]. In contrast to mainstream Strategic HRM, a Sustainable HRM approach arguably assumes that some conflicts of interest and an imbalance of power between employers and employees is a natural part of the employment relationship. It gives proper consideration to both the study of the political economy of work and the social relations of productivity.
The nature and role of informal social interactions provide an essential dimension of workplace employment relations [80]. Employment relations scholars have long recognised that an informal dimension of collective relations helps shape and lubricate the employment relationship. Informal collective relations apply to a wide range of workplace matters including substantive issues covering conditions of employment and procedural issues under which these arrangements are formed and which, in totality, influence performance outcomes [81]. Previous studies have emphasised the importance of informal employment relations. Marchington et al.'s [82] research, for example, emphasises the importance of locating employee involvement schemes within the wider social context. Another illustration of the importance of informal social relations and the context-dependent nature of employment practices is highlighted in a longitudinal study of Hewlett Packard (HP), which argues that informal practice was often more important than formal systems, "the way in which policies are interpreted and enacted in practice" [83]. Research by Sennett [84] sheds further light on the social dimension of the employment relationship in the contem-porary workplace. He suggests that workers forge informal bonds and friendships with co-workers including managers, and that although these do not transform work into a conflict-free zone, they do help to create civility in the organisation [84].
The term 'employment relations climate' has commonly been used to describe the quality of management-employee relations in the organization [85]. Although the concept of organisational climate is multifaceted, how employees and managers interacted collectively to create the 'climate' of employment relations is considered important because of its role in mediating the link between HR practices and environmental performance outcomes [86]. Underlying these arguments is the axiomatic assumption that employment relationships are embedded within a socio-economic, institutional and societal context. Adopting this perspective, it is argued, helps explain why sustainability initiatives are successful in one context and not another. For example, if the supply chain involves outsourcing to a jurisdiction with weaker environmental regulation the net positive environmental effects may be minimal. In addition to focusing on formal and informal workplace employment relations, there needs to be greater sensitivity to the needs of workers outside the traditional employment relationship [54], and the macro and global structures that can buttress the common interests of workers and employers, or even trade unions and environmental movements [87,88]. Here, therefore, sustainability is examined within a theoretical approach that recognises the dynamics of cooperation and conflict in the employment relationship.

Employee Voice in Sustainable HRM
Employee voice or voice, can be described as the conduit for employees to raise issues and concerns, put forward interests and opinions, as well as ideas to contribute to the organisation decision-making with management [89]. For management it provides an opportunity to put forward ideas, test them with the workforce and receive feedback on employee perspectives on the matters [90]. Employee voice mechanisms between management and employees can vary from formal to informal, and occur at various levels across the organisation. [90]. A pertinent aspect of employee voice that is of particular relevance in sustainability is that voice mechanisms can enable and enact the expressing of ideas, solutions and experiences that are of benefit to the organisation, through joint decision-making processes.
There are glimpses within the sustainable management perspective research that indicate the potential role of employee voice in achieving an organisation's sustainability goals. For example, Boiral's [91] research found the importance of tacit knowledge in environmental management. Because tacit knowledge is difficult to codify and is personal in nature, having channels for employee voice has the potential to provide a mechanism for employees to express and communicate their tacit knowledge about the environment, and sustainability initiatives more broadly. Hanna et al. [39] found "employee involvement team projects can be a key source of environmental improvements", reinforcing the point that employees can directly influence sustainability achievements. Recent research on leadership for sustainability has emphasized that leadership is not a position held by an individual, but rather a "characteristic demonstrated by both individuals and teams through an organization in reactive processes" [92]. Concurrently, research argues that a servant leadership style is ideally suited for effectively embedding sustainability in organizations [93] and servant leaders can act as catalysts to foster employees' innovative behaviour [94] and green behaviour [95]. A servant leadership style is seen to be effective for encouraging employee voice in sustainable HRM because of the principle that it should develop followers in such a way that they would themselves "emerge as servant leaders" [95]. Through the theoretical lens of followership [96], those not occupying a formal leadership role (i.e., employees) engage with formal leaders and can therefore also affect pro-sustainability change within organizations through a bottom-up process and, as a result, effectively demonstrate sustainable leadership. From this perspective, followers can take on a sustainable leadership role by co-creating more innovative sustainable initiatives for their organisations [97]. Such research indicates that an employee's perspective on achieving sustainability may further contribute to organisational knowledge, innovation and ability to achieve success in this area. We argue that employee voice is a strategic mechanism that can bridge this gap, if correctly constructed and embedded within the organisation. The following section looks to develop this framework in the context of sustainable HRM.

Finding Voice in Sustainable HRM
Embedding employee voice in the context of sustainable HRM, we argue, is critical in building a relationship between the three pillars of sustainable HRM (financial/economic, social, and ecological/"green"), and maintaining this into the future, a fundamental aspect of sustainable HRM theory [4]. As such the quality rather than the quantity of voice channels is central to successfully establishing these relationships. As with Cox et al. [21], we argue that rather than simply counting the channels of voice, does not allows for insight into the depth and by inference quality of voice. It is by examining how embedded the involvement of the employee is, will, potentially be open the potential in prompting effective sustainability HRM policies and practices.
A key potential problem in this process is the array of voice channels for involvement and participation. In addition, as noted, these processes can be formal or informal and range from the individual or direct employee level through to union representation (indirect) or a hybrid or combination of these channels [90]. As such the degree and participation, involvement and influence can vary within one organisation [21,98]. A second issue is the rhetoric and reality of employee voice, or what Cullinane and Donaghey [99] identify as constructed silence. This occurs where management builds voice channels but, either intentionally or unintentionally due to time, resource and/or skills constraints, creates a culture of employee silence through institutional structures which place constraints on employee voice, supported by pseudo or lip-service voice mechanisms or "deaf ear" [100]. The deliberate or otherwise, discouraging or managing out of employee voice will likely impact seriously on the development of sustainably HRM, by undermining the employment relationship [101], if this is allowed to become the norm. Indeed, it can lead to increased employee self-censoring, conflict and resistance [102], the exact opposite required for sustainable HRM [103]. A key factor in this context also, is that a management, intolerant of critical feedback, deliberately use their (social) power or social exchange to enable a culture of silence to develop [104].
This issue of the rhetoric and reality of employee voice focuses the success or otherwise of such policies and practices, not least on sustainable HRM, and its impact on organisation climate [105]. Organisation climate in this context can be seen as the quality and characteristics of the relationship between management (responsiveness) and the workforce [89,106], as viewed through the lenses of atmosphere, norms, attitudes, behaviours and management workforce relations [89,107]. The key with regard to voice in this context, is to accept that different groups and levels within the organisation bring different perspectives to issues and this should be seen as both a strength and opportunity to enhance change rather than a threat or challenge to be silenced [85,108].

The Paradox of Participation
Whilst issues of silence are increasingly emerging in the voice literature highlighting the rhetoric of voice see [109], it is important that the potential rhetoric of sustainable voice is also acknowledged in the context that we are inundated with claims of, for example "clean" coal and other bizarre statements as organisation clamour to be seen as proactive clean and green. Two theories on participation are particularly salient here. The work of Ramsay [110,111] and his theory of cycles of control which highlighted management interest in employee participation being linked to the power relationship between the two, when employee power (perceived through trade unions) was strong, it was used to negate this power and waned with a decline in employee power and influence. As such participation (as with much of the research on employee silence) cast voice as superficial or management rhetoric [112]. Arguably, when considering genuine voice Marchington's [113] waves thesis, identifies a paradox of participation during a sustained period of decline in the power of organised labour, and attributed this to increased competition and recognition of the knowledge and skills the workforce can provide to enhance the organisations competitiveness and survival. A position supported by Boxall and Purcell [22] and Poole et al. [114] who argue for the need to tap into the potential and diversity in employee knowledge through a variety of participatory and representative structures at the workplaces. In the context of sustainability, Hyman [115] argues that voice is intertwined with other social and economic features and Dundon et al. [116] make the case, employee voice is a process to facilitate the management of external regulatory pressures in driving participation through enhancing productivity and employee commitment [22]. As such the drive to find more sustainable ways of working can result in increased focus on the voice systems. However, as we argue management attitudes is critical in determining the quality and embeddedness of employee voice in terms of genuine participatory processes. A key issue we develop in this conceptual paper.

Conceptualising the Role of Voice in Sustainable HRM
This leads us back to the issues raised by Cox et al. [21] in terms of the quality as opposed to the quantity of voice mechanisms as the central issue. In this context we use the framework of the "escalator of participation" developed by Marchington and Wilkinson [117] to provide the conduit for the development of quality employee voice mechanism based upon the criteria identified above. As Figure 1 illustrates as a graphical continuum, employee involvement and participation is framed in the context to which the workforce is empowered within the context of the breadth and depth of the channels of voice. In this context we have developed the model to add the critical aspects of management culture and style.

Implications and Future Research Directions
The framework of breadth and depth of employee voice channels developed by Cox et al. [21], combined with Marchington and Wilkinson's [117] "escalator of participation" allows for a more nuanced understanding of the complex issues associated with employee involvement and participation and therefore a way to measure the development of voice The "escalator of participation" framework provides a method of evaluating the breadth and depth of voice, the levels at which voice occurs, rather than focusing on the form of employee voice mechanism [118]. As Marchington and Wilkinson [117] argue this framework allows for each type of voice channel to be examined in the context of the degree of input in organisational matters; the participation level within the organisation where the dialogue takes place; the scope of the topics up for debate; and what form of involvement (upward, downward or participatory) and style, be it direct, indirect or hybrid voice, in this case, in relation to sustainable HRM practices. It also implies a level of increased trust and reduced silence as you move up the escalator providing the potential for a more nuanced understanding of the quality of voice being developed.

Implications and Future Research Directions
The framework of breadth and depth of employee voice channels developed by Cox et al. [21], combined with Marchington and Wilkinson's [117] "escalator of participation" allows for a more nuanced understanding of the complex issues associated with employee involvement and participation and therefore a way to measure the development of voice not least for emerging issues such as sustainable voice. In understanding how effective sustainable HRM could be within an organisation this approach allows for the mapping of the effectiveness of communication channels and the understanding of the potential interference and obstacles such as workplace culture and climate, as well as skills to enable organisations to address these issues. Such work would expand on Benn et al.'s [44] finding of the impact of "sustainability cultures" on achieving sustainability goals. This is important if sustainable HRM is not to be seen as a fad but a critical development in the role of HRM in developing the organisational capacity both internally and within the context of the external environment in the 21st century.
The suitability of this framework for exploring employee voice within sustainable HRM is reinforced by the research of Markey et al. [10,45]. Their research found support for Cox et al.'s [21] findings that the breadth and depth of employee voice mechanisms is important within the context of carbon reduction strategies across a range of Australian organisations. A limitation of their research is, arguably, a greater focus on breadth, resulting in the number and combinations of voice mechanisms given focus over the quality and/or effectiveness of said voice mechanisms. Further, their research concentrates solely on carbon reduction strategies under the banner of Green HRM, rather than a broader sustainable HRM exploration. Our proposed framework using the Marchington and Wilkinson 'escalator of participation' would encourage a more nuanced consideration of both the quality and quantity of voice mechanisms in relation to sustainable HRM, and potentially, a mechanism by which various organisation and industry approaches within this field could be compared and contrasted over time. It also provides a road map for organisations to better gauge their level of and quality of voice.
Future research should look to case studies of organisations undertaking sustainable HRM policies and practices and examine the levels and effectiveness of communication channels in the context of implementing sustainable HRM policies and practices successfully. Application of the framework within a case study setting would allow for classification and comparison of various clusters of voice channels within the context of sustainable HRM, revealing useful information not only about variations within voice, but also the impact of and variations across industry, size and other defining characteristics of organisations striving towards sustainability. Although the existing sustainable HRM literature has provided examples of how HR practices improve social and environmental outcomes, methodologically, there is the problem of establishing the direction of the relationship or "reverse causality" [119,120]. Organisations operating as a monopoly or in favourable market conditions will both be able to meet the cost of sophisticated sustainable HRM systems and invest in them. More research is required that measures the sustainable HRM-performance relationship. As Davis and Coan [121] note, to evaluate the effectiveness of change programmes, successful criteria need to be carefully selected to reflect the aim of improving environmental sustainability. A distinction needs to be made between simply counting the number of new sustainability initiatives being introduced and the measuring resulting impact on the organisation and the environment [122,123]. As sustainability becomes an important facet of a wider range of businesses, as evidenced by the rise of certifications, such as B-Corp [124], and an opportunity for competitive advantage, developing a deep understanding of the role of the employee through sustainable HRM will assist organisations achieve their economic, social and environmental obligations and goals.

Conclusions
This research focuses on the often-overlooked role employee voice can play in the development of new management systems and the important role HRM has in both the implementation of new policies and practices like sustainable HRM and the infrastructure such as employee voice to facilitate and maintain such work patterns and practices. Without such an approach sustainable HRM risks being seen as a fad and does not reach its potential within the organisation. This research paper also highlights the potential problems and pitfall associated with the development of effective voice mechanisms and provides a blueprint for the effective development of such work patents and practices.