Casting directors seeking to unionize have sounded threats of a strike as early as next month, after a show of support Wednesday from a wide swath of Hollywood labor.

A news conference at the Writers Guild Theater in Beverly Hills drew about 300 supporters, with “Will & Grace” star Megan Mullally and Oscar winner Marcia Gay Harden speaking in solidarity with the casting directors.

“It seems insane that we are here at all,” Harden said. “But you have to fight for all things that are worthwhile, so let’s fight.”

Mullally said the casting directors — who have asked to be repped by Teamster Local 399 in Los Angeles and Local 817 in New York — are virtually the only sector of below-the-line show business labor not unionized. “This must change,” Mullally said.

Support campaign included endorsements from Tim Allen, Woody Allen, Drew Barrymore, Warren Beatty, Annette Bening, George Clooney, Joel and Ethan Coen, Danny DeVito, Cameron Diaz, Taylor Hackford, Samuel L. Jackson, David Koepp, Ang Lee, Michael Mann, Mike Nichols, Neal Moritz, Lynda Obst, Natalie Portman, Tim Robbins, Gary Ross, Joe Roth, Martin Scorsese, John Singleton, Kevin Spacey, Ben Stiller, Meryl Streep, Hilary Swank, Denzel Washington, Reese Witherspoon and Kate Winslet.

Event also drew support from SAG, AFTRA, DGA, WGA and the Los Angeles County Federation of Labor.

Teamster officials added a feisty touch to the event, insisting they will not back down despite the threat of legal action by the Alliance of Motion Picture & Television Producers.

“We are here to do what we have to do to get the job done,” said Leo Reed, Local 399’s secretary-treasurer. “All that matters is how hard we can kick their asses.”

Though the Teamsters’ contract with the AMPTP includes a no-strike clause, it’s possible that individual members may refuse to work if the casting directors walk out. Teamsters Intl. VP James Santangelo noted Southern California Teamsters had refused to make deliveries for several months during the 2003-04 strike by supermarket workers against Vons, Ralphs and Albertsons.

“If we stick together, we will kick their ass,” Santangelo added.

Local 399 represents about 4,100 employees in Hollywood, mostly studio drivers along with location managers and scouts.

Counter warning

AMPTP president Nick Counter warned Wednesday that the Teamsters could face a lawsuit for violating their contract if their drivers refuse to work during a strike by the casting directors. He noted the contract includes language that bars the union from striking, picketing or boycotting the producers.

“The Teamsters are under a mandate to tell their drivers to go to work,” Counter added.

Indeed, all the showbiz unions have clauses in their AMPTP contracts banning sympathy strikes.

The Teamsters will meet informally with the AMPTP on Tuesday. Local 399 business rep Steve Dayan said a job action could be launched shortly thereafter if the producers refuse to grant recognition to the Teamsters as the bargaining agent.

In previous informal meetings, Counter has offered to request that casting directors be included in the Motion Picture Industry Pension & Health Plan via a nonaffiliated agreement that would obligate employers to make pension and health contributions. Counter said the arrangement would operate in a manner similar to that of several other non-unionized groups, such as members of the Producers Guild of America and production accountants, and could be set up fairly quickly.

Pact security

But the casting directors want the security of a union contract — a step Counter asserts is illegal since most casting directors are independent contractors rather than employees. He’s previously warned that the AMPTP may take legal action against the Teamsters on the basis that combining in an effort to affect the prices paid for their services is unlawful under federal antitrust laws and a wide variety of state laws.

Gary Zuckerbrod, president of the Casting Society of America, asserted Wednesday that casting directors function as employees rather than independent contractors. “What we are seeking is long overdue,” he added.

Studios and nets also face the outside possibility of a work stoppage by actors this summer after their union contract expires June 30. Leaders of SAG and AFTRA have reached a new three-year deal, but the terms have generated significant opposition, and the ratification campaign is expected to be heated.