SAG leaders have said they will send out strike authorization ballots early next month asking members to vote "yes" because the guild's negotiations with the Alliance of Motion Picture and Television Producers are at a standstill.
The AMPTP has maintained that a package it presented June 30 is comparable to pacts made with other guilds in a better economy.
Variety.com said Monday dozens of celebrities, including Matt Damon, Alan Alda, Jason Alexander, Alec Baldwin, Steve Carell, Sally Field, Helen Hunt, Diane Lane, Helen Mirren and Charlize Theron, have signed the letter to SAG leaders.
"We feel very strongly that SAG members should not vote to authorize a strike at this time," Variety.com quoted the letter as saying. "We don't think that an authorization can be looked at as merely a bargaining tool. It must be looked at as what it is -- an agreement to strike if negotiations fail. ... We support our union and we support the issues we're fighting for, but we do not believe in all good conscience that now is the time to be putting people out of work."
Notable deaths of 2014 [PHOTOS]
Polly Bergen, Emmy Award-winning actress, dies