conducting a number of brief strikes over workplace conditions, but avoiding any large-scale confrontations. That changed on January 23, 1937, when the Brooklyn–Manhattan Transit Corporation (BMT) fired two union members at the Kent Avenue powerhouse plant in Williamsburg, Brooklyn for union activity. The union launched a successful sitdown strike two days later that solidified the union's support among BMT employees, helped lead to its overwhelming victory in an NLRB-conducted election among the IRT's 13,500 employees later that year and helped bring thousands of other transit employees into the union. TWU leadership In 1936, the TWU joined the International Association of Machinists to link itself to the AFL. On May 10, 1937, the TWU severed relations with the Machinists and joined the Congress of Industrial Organizations (CIO) as a national union. The union soon faced challenges within, as dissidents within the union and the Association of Catholic Trade Unionists outside it challenged the CPUSA's dominant position within its officialdom and staff. The CP at that time had almost complete control over the union's administration and CP membership was necessary both to get a job with the union and to rise through its ranks. Former allies such as O'Shea attacked Quill and the CP, both in the publications of rival unions, such as the Amalgamated Association of Street Railway Employees, and in testimony before the Dies Committee. Quill and the union leadership gave their opponents all the ammunition they needed by following the changes in the CPUSA's foreign policy, moving to a militant policy after the Molotov-Ribbentrop pact in 1939, then coming out against strikes after the Nazi invasion of the Soviet Union in 1941. Quill shrugged off most of this criticism from outside, haranguing the Dies Committee when it attempted to question him, and disposed of his internal critics by bringing union charges against more than a hundred opponents. The union faced more serious challenges at home as Mayor Fiorello La Guardia threatened to revoke the union's status as the representative of the employees of the IRT and BMT when the City bought those lines in 1940. Quill had cooperated with La Guardia when the former ran, successfully, for City Council in 1937, as a candidate of the American Labor Party. In 1940, however, both La Guardia and Quill became bellicose opponents of each other, with Quill calling a bus drivers' strike that served to demonstrate the union's power if challenged