The war mobilization dramatically expanded union membership, from 8.7 million in 1940 to over 14.3 million in 1945, about 36% of the work force. For the first time large numbers of women factory workers were enrolled. Both the AFL and CIO supported Roosevelt in 1940 and 1944, with 75% or more of their votes, millions of dollars, and tens of thousands of precinct workers. However, Lewis opposed Roosevelt on foreign policy grounds in 1940. He took the Mine Workers out of the CIO and rejoined the AFL. All labor unions strongly supported the war effort after June 1941 . Left-wing activists crushed wildcat strikes. Nonetheless, Lewis realized that he had enormous leverage. In 1943, the middle of the war, when the rest of labor was observing a policy against strikes, Lewis led the miners out on a twelve-day strike for higher wages. The bipartisan Conservative coalition in Congress passed anti-union legislation over liberal opposition, most notably the Taft-Hartley Act of 1947. A statistical analysis of the AFL and CIO national and local leaders in 1945 shows that opportunity for advancement in the labor movement was wide open. In contrast with other elites, the labor leaders did not come from established WASP families with rich, well-educated backgrounds. Indeed, they closely resembled the overall national population of adult men, with fewer from the South and from farm backgrounds. The union leaders were heavily Democratic. The newer CIO had a younger leadership, and one more involved with third parties, and less involved with local civic activities. Otherwise the AFL and CIO leaders were quite similar in background.. How many people, in millions, did union membership expand between 1940 and 1945?