The intervention of the European Union in the field of labour migration is facing a tension between federalisation and decentralisation. While cooperation on migration matters is needed, Member States are reluctant to act in common when it comes to labour migration. Labour migration is indeed linked to socio-economic parameters which are different from one country to another, and it is a sensitive field for national sovereignties. This raises the following questions: what should the EU do in the field of labour migration? Where is there an added value compared to national policies? In my doctoral research, I'm first looking at the origins and the purposes of the EU competence in the field of labour migration. In a second part, I look at secondary law and whether EU law has achieved any added value in conformity with the principle of subsidiarity. The third part is more prospective and based on a camparison with Canada where immigration is also a shared competence between the federal state and the provinces. It discusses potential actions that could overcome the tension between federalisation and decentralisation.