Repression of the North American trade union movement dates to the late nineteenth century. Much of this repression has occurred in response to union militancy during strikes, some of which were directed against political radicals of various orientations. Peaks of repression against radical trade unionism occurred during World War I and in the immediate postwar years as well as in the early Cold War period, after World War II’s conclusion into the early 1950s. Through the analysis of three recently published volumes, I argue that the repression of North American left-wing unions was intentionally severe because of the strength of these labor organizations and the threat they were perceived to pose to employers and the government. Given that these left-wing unions were much more militant than the American Federation of Labor unions, this governmental repression (as well as that of other forces) can be viewed as a conscious set of tactics invoked that were meant to break, or at a minimum tame, these radical unions in the service of capital. Such behavior also acted as a warning to nonradical unions that repression could be directed against them as well.