In this study I analyze the radical mobilization cycle sustained by the Salvadoran Labor movementbetween 1977 and 1981. In these years, Salvadoran organized workers were key contentious actors in what developed into a “revolutionary situation”. To explain this process, this research employs a framework that combines insights from labor studies and social movements about the Global South. From labor studies, I draw from the literature of the contemporary transformation of the labor movement toward Social Movement Unionism (SMU), with a more activist and political profile. According to this perspective, labor movements following an SMU strategy have expanded their demands beyond work-related issues, forged alliances with communities and other contentious forces, widened the range of tactics employed, and combined institutional and non-institutional channels of actions. And from social movement studies, I consider, on one side, the process of inducement of mobilization from economic and political threats. From the other side of civil society agency, I examine the role of preexisting mobilization structures in enabling radical labor actions. Following an integrative model at the subnational level (combining organizational and structural dynamics), I argue that unions and other forms of labor organizations in El Salvador sustained a radical form of SMU protest when previous pro regime structures weakened under a hostile environment of transnational production and repression. These findings are based on the results of a cross sectional and time series study over 8 semesters and across 33 municipios (local units) where labor-based organizations were most active. Using negative-binomial mixed effects models, I find an increase in the likelihood of radical SMU labor actions with acts of state-sponsored repression, and heightened levels of transnational production. Radical forms of SMU protest were less likely to occur in localities with preexisting pro-regime labor unions.