The EU's flexicurity approach to labour market policy promised advantages for trade unions but also posed challenges, given their weak situation in policy formulation at EU level and in many member states. This article explores the potential for union mobilisation on flexicurity and unions' capacity to influence policy debates and outcomes in two member states. In the UK, flexicurity has low political salience and unions' weakened voice has given them little capacity for mobilisation or influence, although they have linked flexicurity to campaigns on agency workers and restructuring. In France, unions have developed alternative proposals on making employment pathways secure and have succeeded in shifting debate towards these proposals rather than the Commission's flexicurity recommendations, although divergence between the positions of unions, employers and the state have limited outcomes to date. Unbalanced or instrumental application of flexicurity measures tends to erode rather than promote trust between social partners, in line with wider developments across member states. EU policies provide only weak leverage since trade unions' ability to influence labour market policy depends on their position within domestic institutions.