Worker migration across EU member states’ borders constitutes an increasingly salient issue. Unlike the liberalization of trade in goods, it has spilled into other policy areas in many unexpected ways. It contributed to turning the so called Bolkestein Directive on services into a highly politicized policymaking episode. Subsequent decisions adopted by the Court of Justice of the European Union (CJEU) have only aggravated looming conflicts between high  and low standard countries, new and old member states, competing social partners and political parties within the European Parliament. Policy issues that are resolutely foreign to EU competences, like the right to strike, have been affected as well. Simply put, recent policy developments about worker migration illustrate the increasingly contested nature of European integration. In that context, decision makers are trapped into a prisoner’s dilemma that is a real or perceived risk arising from regulatory competition. Hence, member states’ preference heterogeneity translates into an amplified risk of policymaking deadlock. Therefore, the question that this dissertation aims to answer is: under which conditions can EU institutions collectively negotiate positive policy solutions in the context of regulatory competition? Taken in isolation, a change in member state’s bargaining attitudes is unlikely and puzzling. Instead, I argue that when there is a high risk of deadlock in the Council the successful negotiation of policy instruments depends significantly on the relative homogeneity of preferences of competing social partners and their ability to defend pan‐European interests next to national immediate interests. The empirical analysis examines four cases of policy negotiations in relation to worker mobility within the EU. Negotiations over the 2006 Services Directive are sliced into two distinct strategic interactions. In addition, I examine the failed negotiations over the 2012 Monti II Proposal on the right to take collective action and the successful negotiations over the 2014 Directive on the enforcement of the 1996 Posted Worker Directive. The selection of cases aims to carry out a conceptual experiment in which the strategic setting is maintained relatively constant while variations in actors’ preferences and strategies may affect policy outputs.