The French labor movement, and especially the main trade union (CGT), suddenly demanded the banning of lead paint, responsible for industrial poisoning of house painters, at the beginning of the 20th century. This article discusses the late and sudden emergence of occupational health in trade union strategies. The issue became a temporary tool to mobilize workers as exemplified by the 1906 painters’ strike in Lille (northern France). The white lead issue boosted the visibility of key figures such as Abel Craissac and provided an opportunity to scale up local collaborative experiments between doctors and workers (Lille). These figures and experiments were clearly at odds with the prevailing union views before WW1. They played an active role in reform dynamics, making the fight against lead paint a major step in the development of a new attitude towards health in the workplace.