In this article, we compare recent innovative union campaigns: the ‘sans papiers’ campaign in France and the ‘Justice for Cleaners’ campaign in the United Kingdom, both based on a sustained grass‐roots mobilization of immigrant workers. Rather than focusing on the ‘usual suspect’ explanatory factors, such as contrasting national settings, union power structures or traditions, our cross‐national comparison highlights important underlying similarities in unions' strategic responses to a growing precarious immigrant workforce. In the absence of established channels of representation, both unions decided to act like social movements fighting for social protection. Using Polanyi's framework, we view both case studies as examples of countermovements against heightened levels of global liberalization and precarious employment.