Questions of justice in the transition to a green economy have been raised by various social forces. Very few proposals, however, have been as focused and developed as the “just transition” strategy proposed by global labour unions. Yet, labour unions are remarkably absent from discussions of the transition towards a green economy. This is surprising as labour unions are arguably the largest organizations in the world fighting for basic rights and more just social relations. This paper tries to advance the potential contribution of labour unions in this arena by asking: what is the full scope of “just transition” today and how have labour unions developed and refined it over the years to render the move towards a green economy both environmentally and socially sustainable? The concept of just transition is hotly debated within labour unions and has different interpretations, and hence different strategies. The last section assesses these interpretations by means of a normative framework, which seeks to fuse political economy and political ecology. Empirically, we add to the growing literature on labour environmentalism, as well as transitions more generally. Analytically, our goal is to place the various approaches to a “just transition” within a heuristic framework of environmental justice that is explicit about power relations when demanding justice, two themes central to this special issue.