This article examines how Corsican nationalism reshaped trade union practice through the Sindicatu di i Travagliadori Corsi (Corsican Workers’ Union, STC), founded in 1984 after local activists broke with mainstream French confederations. Drawing on archival sources and oral histories, it traces the STC’s evolving stance toward immigration and non-Corsican workers during the turbulent 1980s. The union initially pursued an openly ethnic agenda – ‘Corsicanization of jobs’ – that framed mainland French migration as settler colonialism and sought to reserve employment for native islanders. By the decade’s end, however, the STC had reframed this demand as a call for equal opportunity for all workers living in Corsica, formally abandoning ethnic membership rules and admitting to its ranks workers from mainland France and North Africa. Despite this rhetorical shift, North African migrants remained marginal: they joined in small numbers and never reached leadership positions, highlighting persistent racial segmentation in Corsica’s labour market. The case of the STC illustrates a form of ‘conditional universalism’, in which formal inclusion depends on alignment with nationalist goals, offering new insight into the coexistence of class solidarity and minority-nationalist politics on Europe’s periphery.