Despite increasing interest in the impact of social movements that target private firms, we know little about the emergence of such movements. Social movement theory situates such emergence in the context of larger protest cycles but has not tested the idea. We theorize about the determinants of 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 American cities around issues like Civil Rights, the Vietnam War, and the women's movement; and subsequent support for labor-union organizing in those cities. We combine nationally representative data on protest events from 1960 to 1995 with data on every union-representation election held from 1965 to 1999. We find that greater levels of (lagged) protest activity are associated with greater union support; that such osmotic mobilization is greater when there is substantive overlap between the claims of the two parties; and that the extent of mobilization varies with the opportunity structure within private firms. We discuss the implications of ideological and interest overlap as a contingent factor in future research on the emergence of mobilization targeting private firms.

Despite increasing interest in the impact of social movements that target private firms, we know little about the emergence of such movements. Social movement theory situates such emergence in the context of larger protest cycles but has not tested the idea. We theorize about the determinants of 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 American cities around issues like Civil Rights, the Vietnam War, and the women's movement; and subsequent support for labor-union organizing in those cities. We combine nationally representative data on protest events from 1960 to 1995 with data on every union-representation election held from 1965 to 1999. We find that greater levels of (lagged) protest activity are associated with greater union support; that such osmotic mobilization is greater when there is substantive overlap between the claims of the two parties; and that the extent of mobilization varies with the opportunity structure within private firms. We discuss the implications of ideological and interest overlap as a contingent factor in future research on the emergence of mobilization targeting private firms.