he CIO's first major victory in Canada came in April 1937 at the huge General Motors (GM) plant in Oshawa. Management refused the demands of its 4,000 workers for an eight-hour day, better wages and working conditions, a seniority system, and recognition of the United Auto Workers (UAW), their new union. On April 8, the workers' struck, launching one of the most significant confrontations in modern Canadian labour history. Although the workers struck over local issues, GM management and Ontario Premier Mitchell Hepburn worried that a victory in Oshawa would greatly increase the popularity of the Committee for Industrial Organizing (CIO) throughout industrial Ontario. After two weeks, GM settled the strike — much to the annoyance of the provincial government. Management recognized that the depth of union support would be difficult to overcome, and it feared the loss of markets a protracted strike would entail.

The union won many of its demands. On the key issue of union recognition, GM accepted collective bargaining, but union leaders had to first publicly sever ties with the CIO. Despite such official statements, many recognized the Oshawa strike as a significant CIO victory. The Oshawa UAW was a made-in-Canada union, like most CIO affiliates that emerged in the next decade. They were organized by Canadian workers over Canadian concerns and led by Canadians. They affiliated with the CIO unions in the United States, because of the energy of the CIO in the 1930s and 1940s, and because of the fact that they worked in the same industries for the same employers, and under similar conditions.