To examine whether and how social movements that target private firms are influenced by larger protest cycles, we theorize about osmotic mobilization--social movement spillover that crosses the boundary of the firm--and how it should vary with the ideological overlap of the relevant actors and the opportunity structure that potential activists face inside the firm. We test our hypotheses by examining the relationship between levels of protest in U.S. cities around issues like Civil Rights, the Vietnam War, and the women's movement and subsequent support for labor-union organizing in those cities. Combining nationally representative data on more than 20,000 protest events from 1960 to 1995 with data on more than 150,000 union organizing drives held from 1965 to 1999, we find that greater levels of protest activity are associated with greater union support, that spillover accrued disproportionately to unions with more progressive track records on issues like Civil Rights, and that these effects were disproportionately large in the wake of mobilization around employment-related causes and shrank in the wake of conservative political reaction that limited room for maneuver among the external protesters, the labor movement, or both. Our research helps to specify the channels through which external pressures affect firm outcomes.
