This paper analyzes the 1939–1940 New York World’s Fair as a conflicted site of public-sphere formation, and the repercussions of these conflicts on organized labor in New York. Conceived within the liberal administration of Mayor La Guardia and dedicated to the principles of social cooperation, this “closed-shop exposition” granted American Federation of Labor (AFL) trade unions an unprecedented degree of workplace benefits and rhetorical support by the Fair administration. This was undermined, however, by the trade unions’ limited public activities within the fair itself and their refusal of city offers to establish outreach and educational programs through events, rallies, and pavilions. As a result, the public space and discourse of a fair nominally devoted to social interdependence was appropriated by a variety of other interests, particularly those of corporate America. This marginalization would ultimately contribute to delegitimization, as allegations of graft and racketeering by visitors, exhibitors, and the national media framed labor as a direct threat to the “World of Tomorrow” and its visitors. Millions of Americans found their visits marred by exorbitantly inflated prices, delayed by strikes, and disappointed by cancelled exhibits. In the face of outside pressure, and with labor groups unable to address hostile critiques within the fair itself, the exposition administration withdrew its public support for unions while dramatically restricting their workplace rights. In this way, the “business-union” principles of the AFL not only undermined their legitimacy in the eyes of the public, despite the efforts of liberal municipal officials to promote them, but ultimately served to undo those very workplace gains such principles were meant to secure.