This article explores the effects of borders on the making of trade union policies and on their capacity to act. It takes as an entry-point the reform of Luxembourg's system of family allowances and financial support for students in 2010, which redefined the group of beneficiaries and partly excluded cross-border workers from neighbouring countries. This led to heated debates in Luxembourg and in the Greater Region (comprising Luxembourg, Saarland, Rhineland-Palatinate, Lorraine and Wallonia) during which trade unions played an important part. The author explores the contradictory logics of both competition and cooperation within the Greater Region. These lead to a gap between integration as a discourse and what it means for local populations, in particular regarding labour market competition. The debates within trade unions on the issue of social entitlements for cross-border workers offer insights into the dynamics of this dichotomy and into the everyday fabric of cross-border social relations.