In the eight years prior to the attack on Pearl Harbor, the American labor movement had experienced the greatest growth and most dramatic changes in its history. The number of workers in trade unions had increased from under three million at the beginning of 1933 to over ten million by the end of 1941. The Congress of Industrial Organizations (CIO) had come into existence, initially as a split from the American Federation of Labor (AFL) in 1935, to organize unskilled and semi-skilled workers in mass production industries on an industrywide basis—mobilizing hundreds of thousands in steel, autos, electrical appliances, meat-packing, and other basic industries.

In the mainstream American labor movement, the CIO had also represented a new kind of unionism previously associated with radicalism in the form of socialism and communism. In this "social unionism," labor unions actively involved themselves in politics—supporting public...