Academic interest in Global Framework Agreements (GFAs) has grown considerably over the past several years, but the focus has largely been limited to comparing their various clauses and provisions. More recent research has centred on case studies of their implementation. In this article, we move beyond an exclusive analysis of GFAs to a broader conceptualization of steps towards globalizing labour relations, in which GFAs are fundamental. In our heuristic model, a GFA is the negotiated result of interest representation. A GFA creates an arena for the pursuit of global labour relations by defining the content, selecting the actors, delineating the processes and setting the boundaries of labour-management interaction. As a political space undergoing institutionalization, all of these dimensions of arenas are still contested. Although the structural boundaries are fuzzy at the periphery, such arenas reach beyond the organizational entities of the signatory transnational corporation (TNC) to encompass the global production network (GPN). Furthermore, we show how Global Union Federations (GUFs) and their member unions operating in regard to particular GPNs have begun building Transnational Union Networks (TUNs). Using two very different case studies, we argue that structural contingencies and strategic choices intertwine to bring about divergent TUN trajectories: one favouring a limited company-specific internal approach, the other a broader, GUF-led union-building approach. As exemplified by these findings, TUNs in our construction of an arena linking key elements of transnational labour relations are still 'work in progress'. Our concluding hypotheses reflect this contingency and the need for further research.