Building on recent scholarship that highlights social change caused by the Anti-Japanese War, this paper traces the politicization of women working in the cotton mills of Chongqing, the Nationalist wartime capital. Upon joining the workforce in the late 1930s, most cotton mill hands were young, uneducated women expected to endure hard work and remain physically confined to the factories. By 1945, women workers were at the forefront of a militant labour movement, writing manifestoes and petitioning government officials. This process of politicization stemmed from their decision to work in factories, which breached societal norms, and their experience of disciplined labour regimes and brutal working conditions, which fostered an incipient class-consciousness. Moreover, Nationalist-sponsored factory education campaigns had the unintended effect of leading women to challenge class exploitation and sexual discrimination. Their participation in the labour movement, which was fuelled by their struggle for economic justice and desire for higher social status, used both legal forms— especially petitions and letters to the press couched in the wartime nationalist rhetoric of shared sacrifice—and extralegal means, namely class violence. The paper concludes that the social changes and conflict that accompanied women's wartime work helped prepare the terrain for Communist rule.