The Simpsons: D'oh! Homer Simpson and the rest of the mustard-colored citizens of Springfield are on strike.

The actors who do the talking for Homer, Bart and the rest of the cartoon stars of the long-running Fox television show "The Simpsons" are keeping their mouths shut until producers pay them more money, a source familiar with the situation said on Thursday.

The show's six principal voice actors, whose contracts expired several months ago, have refused to show up for script readings during the past few weeks, delaying production on the upcoming 16th season of the animated series, the source said.

The show centers on the antics of a beer-guzzling, doughnut-chomping family man named Homer Simpson, his spiky-haired misfit son, Bart, and all their friends and relations in the fictional town of Springfield.

There was no public comment on the salary dispute from the Fox network or the producers at sister studio 20th Century Fox Television, both units of Fox Entertainment Group Inc. (NYSE:FOX - News), which is controlled by Rupert Murdoch's (News) News Corp. Ltd. (Australia:NCP.AX - News; NYSE:NWS - News).

But the source confirmed a report in Hollywood trade paper Daily Variety that each of the six cast members was demanding a a salary of $360,000 per episode, or nearly $8 million for a 22-episode season. Each actor currently is paid $125,000 per episode, the source said.

While that might seem like a modest sum for a program that has been a signature show for Fox and a linchpin of its Sunday schedule for years, the source said the voice actors essentially work the equivalent of one day per episode.

On the other hand, producers have to wonder whether they could ever replace the familiar voices who utter such popular catch phrases as Homer's anguished exclamation "D'oh!" or Bart's "Ay, caramba."

The highest-paid star on U.S. TV is Ray Romano, who reportedly earns between $1.7 million and $2 million per episode of his Emmy-winning series "Everybody Loves Raymond."

The six "Simpsons" cast members banding together to force a settlement of their contract renewal talks are Dan Castellaneta (Homer), Nancy Cartwright (Bart), Yeardley Smith (sister Lisa), Julie Kavner (family matriarch Marge), Hank Azaria (bartender Moe and Apu the convenience store clerk) and Harry Shearer (Homer's tyrannical boss, Mr. Burns and Bible-toting neighbor Ned Flanders).

The last "Simpsons" work dispute arose in 1998, when the actors were making $30,000 per episode. At that time, the show's producer hired casting directors in five cities to replace most of them before both sides worked out a new deal and resumed production.

This season, "The Simpsons" surpassed the real-life Nelson family on "The Adventures of Ozzie and Harriet" as the longest-running weekly comedy series on American TV. The Nelsons left ABC in 1966 after 14 seasons on the air.

"The Simpsons" currently averages about 12.5 million viewers a week on Sunday nights, down from its peak ratings several years ago, but it remains a critical favorite and worldwide pop culture phenomenon seen in dozens of countries. It also is a cash cow for 20th Century Fox TV for the handsome revenues it generates in U.S. syndication.