Jack Nicholson, Viggo Mortensen, Nick Nolte and other actors will come out in support of the Screen Actors Guild's negotiating team and call for a smaller union to return to the bargaining table in a new ad to run Thursday, said a person familiar with the situation.

The ad, to run in trade publications Variety and The Hollywood Reporter, contains the names of more than 60 actors including Josh Brolin, and Rosanna and Patricia Arquette, said the person, who was not authorized to speak publicly and requested anonymity.

The high-powered endorsement of the union's tactics comes just days after Tom Hanks added his name to a petition calling on actors to endorse a deal reached by the smaller American Federation of Television and Radio Artists.

The battle of lists put a smaller group of guild-supporting stars like Martin Sheen and Holly Hunter against the AFTRA backers who signed onto an online petition at http://www.AFTRAYes.com led by Hanks, Alec Baldwin, Kevin Spacey, and some 600 other lesser-known actors.

The three-year contracts of both unions, covering prime-time TV and movie productions, expire Monday.

AFTRA, which reached a deal with the major Hollywood studios May 28, sent out ballots to members last week to ratify the pact. The results are to be announced July 8. SAG has waged an all-out campaign to oppose the deal, saying the precedent would handcuff its negotiations. It has not yet called for a strike authorization vote.

"In the current issues that we are dealing with, I would say that AFTRA is one of the main stumbling blocks," Mortensen said in an endorsement posted Tuesday on the SAG Web site. "They are not working for actors and SAG is."

The ad says the guild is not finished with its negotiations and calls for higher minimum wages, residual payments for all Internet content, jurisdiction over all productions targeted only at the Web, and an increase in payments for appearances in DVDs.

"We believe AFTRA should go back to the bargaining table, with SAG, and fight for a better contract," it says.

The delay in reaching a contract with SAG, Hollywood's biggest actors union that represents 120,000 members, has thrown a kink in movie production schedules.

Some movie projects have experienced delays in getting approved for shooting, while others have scheduled breaks between shoots in case there is a labor disruption.

AFTRA, with 70,000 members in a handful of prime-time TV shows, issued a statement late Tuesday criticizing the guild for "spending its members' dues in a misguided effort to attack another union and undermine a solid contract."

Some 44,000 actors hold memberships in both unions.

Jonathan Handel, a former Writers Guild of America associate counsel, said SAG's effort to bring AFTRA back to the bargaining table was unrealistic because of the bad blood between the two feuding unions.

The result could be a delay of talks well past the June 30 expiration of the current contract, he said.

"I think we're in this gray sort of Netherworld where we neither have a strike nor a contract for some period of time," Handel said. "There always will be a deal eventually, the question is when."