It is a good bet that Soviet/KGB/Russian money has been going to Marxist/communist/socialist-led American unions since the 1920s. The whole CIO was literally an extension of the Soviet KGB, esp. the UE (United Electrical Workers).
Read the congressional hearings on Communism and Labor from both the House Committee on Un-American Activities and the Senate Internal Security Subcommittee, Sen. Judiciary Committee. It’s all there.
Today’s leftist unions, most spawns of older CPUSA founded/led unions (i.e. Local 1199 Hospital Workers Union; District 65 Distributive Workers, etc - NOW THE SEIU) are heavily socialist/Marxist led. The leader of the AFL-CIO, Richard Trumka, formerly the leader of the United Mine Workers of America, is a hardcore Marxist, with a preference in the old days for the Trotskyite “Socialist Workers Party”. You can read about him in their weekly publication “The Militant”, esp. in the 1970’s and 80’s, before they fell apart.
You'd win that bet: Communists in the United States Labor Movement (1919–37)
Trade Union Educational League
In actuality, the TUEL was a cross between a mass organization and the industrial department of the Communist Party of America, The vast majority of its members up to 1925 were members or supporters of the Communist Party, as Foster noted to the Comintern in 1925. The TUEL was referred to as "The X" in the minutes of the underground CPA organization and was to a very great extend funded by the Communist movement. There were no dues collected for membership as a means of making it difficult for the AF of L bureaucracy or its member unions to purge TUEL adherente from their organizations -- there were no membership cards of any sort -- and the only visible means of financial support of the organization were revenue generated from a series of 10 and 25 cent pamphlets.
"Statement Regarding Funds for T.U.E.L. Received by Party, Moscow, February 23, 1926": The Soviet World of American Communism, p. 127
Yes, but it seems like the roles are changing.