Production has halted after they demanded a threefold increase in their salaries.

Dan Castellaneta is the voice of Homer but he is clearly no mug. Along with his five colleagues he believes the $125,000 (£68,000) he earns for each 30-minute episode does not reflect the true value of the characters.

The six core cast members are now demanding $360,000 (£194,000) an episode or $8 million (£4.3 million) for a 22-episode season, according to insiders.

Production on the sixteenth season of the series, which is watched by 60 million viewers in 60 countries, was halted after the cast failed to show up for script readings.

They may not be household faces but Castellaneta, Nancy Cartwright (Bart), Julie Kavner (Marge), Hank Azaria (Moe, Apu, Comic Book Guy), Yeardley Smith (Lisa) and Harry Shearer (Mr Burns and others) believe that after 16 years their voices are irreplaceable. They could be in for a shock. During a salary dispute in 1998 Fox TV considered firing the actors and hired casting directors in five cities to explore replacements for the “voice talent”.

The cast earned just $30,000 an episode in 1998 and eventually secured an increase. But with each episode of the series now costing $1 million, Fox is determined to keep a tight control on costs.

“They already have the deal of a lifetime,” one executive said, noting that the actors work just six to seven hours to voice a single episode.

Even Ray Romano, the Everybody Loves Raymond sitcom star who is America’s highest-paid actor, works longer hours for his £1.2 million per episode.

Representatives of the actors argue that The Simpsons has become a $1 billion DVD and merchandising industry and that their clients are seeking only payments that reflect their contribution.

Last year Castellaneta said of the cast’s salaries: “I would say, all together, we still don’t make as much as one Friend.”

Their previous three-season deal has expired and with negotiations having drawn a blank, the cast have decided not to return to work.

A lengthy stoppage could disrupt The Simpsons’ broadcast schedule. Each episode takes six to eight months to complete.

Before the dispute, James L. Brooks, the executive producer, praised his “uniquely talented voice people. They are really great comic talent . . . inventive, creative people.” Azaria, the voice of Moe and Apu, has won the best voice-over Emmy award twice in the past three years.

However, career opportunities for the faceless cast may be limited outside Springfield. Castellaneta’s credits include Thing One/Thing Two in the feature film The Cat In The Hat and an appearance as Aaron Spelling in a television film, Behind the Camera: The Unauthorised Story of Charlie’s Angels.

Nancy Cartwright has lent her voice to Rugrats films and appeared in a minor role with Azaria in the 1998 Godzilla blockbuster. Azaria also features in the present box- office hit Along Came Polly.

The Simpsons is watched by 14.5 million viewers in the US. Soaring salaries could threaten an expectation that it will become the longest-running sitcom, should episode 436 be reached in five years.

A deal is further complicated by the announcement that Matt Groening, the series creator, is working on a Simpsons feature film to which the cast members are expected to sign.

Twentieth Century Fox TV, owned by News Corp, parent company of The Times, and James L. Brooks’s Gracie Films, which co-produces the show, declined to comment.

The wisdom of Homer offers one solution. In a 1995 episode he advised Lisa on industrial action: “If you don’t like your job, you don’t strike. You just go in every day and do it really half-assed. That’s the American way.”

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