Unions are key repeat players before the United States Supreme Court. Their involvement goes beyond what one might expect (labor) and extends to key cases involving federalism, discrimination, affirmative action, the First Amendment, and workplace health and safety, among others. Though scholars have documented the effects of other union activity, like collective bargaining, on nonunion workers, the role and impact of union participation in nonlabor litigation has largely been ignored in both the public debate over unions in America and in the academic literature about what unions do. This Article focuses on unions’ Supreme Court litigation that arises outside of the context of traditional labor law in order to show how union-made law affects interests beyond those of the labor movement, its members, and unionized employers. It reveals how union-made law has significantly affected the structure of American government and society. This Article first describes the many areas in which union Supreme Court litigation has had important social effects extending far beyond core labor interests and explains why, as a practical matter, unions are well-situated to bring or fund these cases. Next, the Article explores three characteristics that have the potential to shape unions’ litigation positions: first, unions are more likely than other social movement litigators to litigate defensively as well as offensively; second, unions operate based on majority rule; and third, unions may use litigation as a part of a bargaining strategy. The Article shows how these dynamics have played out in past cases, sometimes with surprising results. Finally, the Article concludes with some observations regarding declining union density in this country.