Actor Sean Penn has urged actors not to vote for a deal proposed by the American Federation of Television and Radio Artists (AFTRA), the CM reported.
The deal on working conditions and pay is aimed at avoiding a potential strike this summer.
But Penn believes the terms are unfair and has sent an email to his fellow 44,000 Screen Actors Guild (SAG) members.
SAG has its own proposal, which it argues is stronger than that negotiated by smaller union AFTRA.
In the email, the 21 Grams actor said: "AFTRA's deal not only falls short of fair compensation and protection for actors but just as significantly reflects corporate appeasement that will have an irreversible negative effect on the integrity of the show and the films we perform in.
"They're trying to buy us out, bully us down and, in so doing, they will destroy the very purpose of our work."
AFTRA's proposal is similar to the deal that ended the writer's strike earlier in the year.
Bosses of both unions have made competing appeals to their members to seek better conditions from studios.
SAG leaders say that defeating the AFTRA deal could help them get a better settlement for all actors under the larger SAG contract.