Vulnerable migrant workers are generally very reluctant to take legal action to challenge exploitation given the many obstacles they face, and instances of such action are important to examine for their exceptionality. This article presents a case study of non-unionised Portuguese construction workers who engaged in a lengthy legal battle against their Portuguese employers for various forms of wage theft while they worked in Ireland. The aim of the article is to assess the extent to which their legal action was an effective form of collective action. To do so, we draw on industrial relations and law literature to explore the purposes of collective action and litigation and apply this understanding to assess the outcomes of the migrant workers' legal cases. We find that the workers' legal action was a partially effective form of collective action that sought to address the source of their discontent. The case study highlights the regulatory dilemmas that arise in an institutional environment where workers ability to engage in voluntarist forms of collective action is constrained and they seek to use the legal system as collective subjects.