Except in the torpid imagination of FBI agents, folk music was not controlled by the Communist Party.
For one thing, folk music is romantic. It is rural and calls for a return to the days before electronic music and large concert halls. It calls for a return to local music and face-to-face relations between musicians and audiences. The Communist Party is progressive and does not advocate going back to a simpler time. As this article points out, the Communist Party had its own problems to contend with and had no time to attempt to control folk singers like Pete Seeger or Woody Guthrie. While some folk singers were sympathetic to the CP, their work was in no way controlled by it.