Bull. They loved it when the central government backed THEIR violations of others' property rights -- that was "justice".
They just opposed the logical extension of their own beliefs and tactics to ALL THE REST OF SOCIETY. Everybody is opposed to the forcible redistribution of their OWN wealth.
It depends what you mean by Communist. American labor unions were firmly united against the USSR and the Communist Party, which was ousted from any posts it held in the unions after the Cold War began. As late as Reagan's time the labor unions helped support the Solidarity Movement in Poland which helped bring down the Soviet Union.
The chief centers of real card-carrying Communists in America after in 1950s and after were among intellectuals, academics, the entertainment industry, and in some branches of government where they had wormed their way in.
That's no longer true. The rank and file members of unions are still mostly social conservatives, but the leaders are flaming leftists. This only happened in fairly recent times.