HOLLYWOOD — Some actors are lining up behind Tom Hanks. Others are backing Jack Nicholson.

HOLLYWOOD — Some actors are lining up behind Tom Hanks. Others are backing Jack Nicholson.

No, this is not an Oscar race. It's the campaign over a new contract for Hollywood actors, and the two stars are on opposing sides.

Welcome to the civil war that has turned Hollywood upside down and is fast diminishing the prospects of a peaceful resolution between actors and studios for a new accord.

With the entertainment industry's major contract with actors set to expire at midnight today, Hollywood is bracing for its second period of labor unrest this year. But this time the turmoil is exacerbated by an ugly family feud that is pitting actor against actor.

In recent weeks the dominant actors' union, the Screen Actors Guild, has mounted a highly unusual campaign to scuttle a new agreement negotiated by the American Federation of Television and Radio Artists. The effort — targeted at 44,000 members who belong to both unions — has split the ranks of actors, with stars lining up on opposite sides as their leaders trade daily barbs in e-mail blasts to their members.

"I've never seen anything like this," said former SAG President Richard Masur, who is a member of SAG's national board. He called his union's campaign "incredibly divisive."

Masur is among more than 600 actors, including Hanks, Susan Sarandon, Kevin Spacey and Alec Baldwin, who signed a letter last week in support of the AFTRA accord, which they describe as a good agreement. "If this deal doesn't pass it will take us to a place from which we may not recover," the actors warned.

SAG, however, has lined up its share of high-profile backers, including Nicholson, Ed Harris and Viggo Mortensen, who delivered a personal message of support posted on the union's Web site.

Then there's a third camp led by George Clooney, who staked out a middle ground by calling on both unions to end their warring and stop "pitting artist against artist."

AFTRA's tentative contract includes pay hikes for actors and is modeled on similar pacts negotiated by writers and directors. But SAG leaders maintain it doesn't address their bargaining goals, including an increase in the residuals actors earn from DVD sales, giving them a say in how products are pitched in TV programs and ensuring that all shows created for the Web are covered under its contracts.

SAG is spending $150,000 in a barrage of ads, automated phone calls and e-mails to urge joint members to vote down the agreement.

The vote, which will be finalized July 8, could be a litmus test for whether SAG has enough support to wage a strike. AFTRA, which has 70,000 members, has called the effort a "politically motivated disinformation campaign."

Regardless of the vote results, it's unlikely the unions will patch up their differences anytime soon. The two unions have clashed for years over which group can lay claim to actors who work in cable television, and now the battle is shifting to the more high-stakes world of prime-time TV.

Although 120,000-member SAG currently dominates prime-time TV and all of feature films, the rival union is poised to capture a number of new prime-time dramas and sitcoms, thanks in some part to friendlier relations with the studios.

That could give AFTRA a level of clout it hasn't seen since the 1970s and 1980s, when the federation represented such hit sitcoms as "The Cosby Show," "All In The Family" and "Facts of Life." It also could pose a serious competitive threat to SAG, given that AFTRA already dominates in cable TV, reality programs and daytime television.

The unions have had an uneasy alliance since 1981, when they formed a joint bargaining pact that recently fizzled after AFTRA accused SAG of attempting to poach one of its soaps, "The Bold and The Beautiful," a claim disputed by SAG and the show's star, Susan Flannery.

Until then, the unions had largely respected each others' jurisdictional boundaries: AFTRA handled shows that are "recorded live," reflecting its origins in radio, and most programs shot on videotape, while SAG had dibs over everything captured on film.

But those lines have been blurred in recent years as more shows are shot with digital technology, supplanting the older formats. Each guild claims jurisdiction over digital, setting the stage for conflict.

Producers and studio executives praise AFTRA for being easier to work with and more willing to tailor contracts that reflect the tight budgets of cable TV shows, which are a fraction of those on network television.

Critics say SAG contracts are more rewarding to actors.

"Analyzing the question as a zero-sum contest between two unions is ridiculous," AFTRA Executive Director Kim Roberts Hedgpeth said. "Our primary concern is making sure that there is work for actors and other performers ... with the protections of a union contract."