This dissertation synthesizes social theory, history, legal doctrine, and original empirical research to uncover the role that law, as dialogically mobilized by social movements over the twentieth century, has played in shaping the socio-political meanings of unionism. I show that law has helped construct labor unions and social movements, and in turn, economics and rights, as having categorically distinct normative stakes. These socio-legal dichotomies continue to inhibit intersectional analysis and coalition-building within contemporary American progressivism.