Through a historic wave of strikes, France’s sans-papiers (immigrants without papers) became known as ‘sans-papier workers’ and renewed their fight for legal status. The state instituted employment-based regularization and unions embraced migrant workers’ access to legal status as a labour issue. Following Bourdieu and Boltanski, this article traces the institutional genesis and political trajectory of the ‘sans-papier worker’ as symbolic category and objective group, highlighting its agonistic coproduction by state policy and union strategy. The study relies on a three-year collective ethnography including participant observation, archive collection and over a hundred interviews with migrant workers, union activists, employers and civil servants. Whereas the new framing initially uncovered the reality of undocumented migrants at work, it gradually became an exclusive category that sorted ‘workers’ from the others. Ultimately, the fight for ‘sans-papier workers’ confronted labour organizations and the state with the question of when one starts and stops being a worker.