This article explores differences in labour conflicts in Italy and France by focusing on the characteristics of the most prominent structures of worker mobilization: trade unions. Despite several similarities between the French and Italian industrial relations systems, and despite the fact that trade union density in Italy is more than three times greater than it is in France, France is one of the few European countries in which the average strike volume increased after the Great Recession. Protests in France also peaked in the pre-crisis period, while Italy did not show any wave of contention. We contend that the nature and level of labour conflicts observed in the two countries in the last two decades depend on alliances between trade unions and other social groups and organizations sustaining worker mobilization, specifically, social movement organizations. In particular, we argue that labour conflicts are related to the characteristics of social movement unionism. Evidence from cases studies in France and Italy suggests that the role of trade unions and their alliances has been different in the two countries. Confederal trade unions in France have been able to engage in social movement unionism within broader coalitions involving other social categories and social movement organizations. In contrast, in Italy, these dynamics have mostly involved small rank-and-file unions and self-organized workers’ groups engaged in radical political unionism. This has resulted in different levels of mobilization associated with social movement unionism and radical political unionism, given the greater capacity of confederal trade unions in building nationally coordinated and sustained collective actions.