Closing Ranks: Organized Labor and Immigration

This paper shows that immigration fostered the emergence of organized labor in the United States. I digitize archival records to assemble the first county-level dataset on historical U.S. union membership and use a shift-share instrument to isolate a plausibly exogenous labor supply shock induced by immigration, between 1900 and 1920. Counties with higher immigration experienced increases in union presence, the number of union branches, the share of unionized workers, and the number of union members per branch. These effects were more pronounced among skilled workers, particularly in counties more exposed to labor competition from immigrants, and in areas with more negative attitudes toward immigrants. The evidence is consistent with existing workers unionizing in response to immigration, driven by both economic and social motivations. These findings highlight a novel driver of unionization in the early 20th-century United States and reveal an unexplored consequence of immigration: the development of institutions aimed at protecting workers’ status in the labor market, with effects that persist to the present.