SAG and AFTRA may merge.

Several high-profile actors, including Ed Asner, Valerie Harper, and Martin Sheen, have gone to court to try and stop the two unions from merging. According to the LA Times, they're doing so because the SAG hasn't done a full study. I don't know anything about union law, but I do know a lot about company law, and, from that perspective, that may not be grounds for a lawsuit, because the courts cannot interfere with the management decisions of the entity.

What the actors can do, IMHO, is to sue on anti-competitive grounds, saying that the merger will restrict competition.