And you are factually wrong.

You are probably thinking about the Communist factions among the Republican forces opposed to Franco.

ALL of the Republican factions were opposed to Franco and to fascism, not only the Communists.

And, besides, nobody was calling themselves "antifa" at that time, because that was damn obvious that if you were in the Resistance, you were opposed to that despicable tyrant. But they were absolutely anti fascists, all of them and not only the Communists.