The major Hollywood studios have told the Screen Actors Guild that if the union does not accept its final contract offer by Aug. 15 any proposed wage increases would not be retroactive, the studios said Wednesday.

The producers alliance threw down that gauntlet in its final offer, which it said included $250 million in additional compensation over three years.

If the deadline passes before the union ratifies a contract, that means the actors could lose more than $200,000 a day in increases dating to July 1, the day the new contract would take effect.

The announcement was made as the two sides appeared to be headed toward an impasse in their contract talks.

"The producers have included this traditional incentive in the final offer in order to get everyone back to work," the producers alliance said in a statement.

Norman Samnick, a lawyer who has represented the studios in talks with actors, said such a clause was not unusual when negotiations extend beyond the end of a contract.

"The companies may use that as a point of negotiation," Samnick said.

A guild spokeswoman declined to comment.

The studios, represented by the Alliance of Motion Picture and Television Producers, plan to meet with the guild Thursday afternoon to discuss their final offer.

On Tuesday, the American Federation of Television and Radio Artists, a smaller actors union with 70,000 members, said it had ratified a three-year deal retroactive to July 1.

The Screen Actors Guild had campaigned hard against the AFTRA deal and claimed that if members approved it that would undermine SAG's ongoing talks.

The guild, which represents 120,000 actors in movies, TV and other media, said late Tuesday that its work at the bargaining table will continue, despite the ratification of the smaller union's deal.

The guild represents the vast majority of work in prime-time TV and movies. Any work stoppage by its members could throw the industry into turmoil, even if AFTRA members continue working.

"We will continue to address the issues of importance to actors that AFTRA left on the table," SAG President Alan Rosenberg said in a statement Tuesday. "We remain committed to achieving a fair contract for SAG actors."

The guild has not called for a strike authorization vote.

In addition to the terms AFTRA approved, the guild said it is seeking further increases in compensation for DVD sales and Internet content and additional terms covering actors who must endorse products in scripted scenes.

But the producers' chief negotiator, J. Nicholas Counter III, said in a letter to California's state Legislature Wednesday that the alliance had presented its "last and best and final" offer to the guild.

The producers' stance left open the possibility they could declare talks were at an impasse. If confirmed by the National Labor Relations Board, the declaration would allow them to impose certain clauses of their offer on the guild, Samnick said.

But most proposed changes between the old contract and the new offer favor the guild, said Scott Witlin, an entertainment lawyer who has represented television networks in the past.

"I can't imagine they would actually implement the wage increases," Witlin said. "That's just giving away money without getting an agreement."

The guild responded to the alliance's letter by saying it wanted to keep talking.

"If anyone is stalling, it's the AMPTP by suggesting that bargaining is over," said deputy executive director Pamm Fair in a statement. "Screen Actors Guild remains committed to bargaining a fair contract, and is available 24-hours a day, seven-days a week."