LOS ANGELES - A musicians union has filed a federal lawsuit against the producers of "American Idol," claiming musicians were underpaid because the show's live music was re-recorded for reruns.

The American Federation of Musicians filed the suit seeking unspecified damages Thursday in U.S. District Court in Los Angeles, alleging that American Idol Productions Inc. and its subsidiary Tick Tock Productions Inc. violated a collective bargaining agreement.

That contract says the show's musicians should be paid royalties for rebroadcasts of the show, the lawsuit said.

The producers are required to pay 75 per cent of scale to musicians who appear in the original show and rehearsals, plus 10 per cent of that pay to a union pension fund, with decreasing percentages for each rebroadcast, according to court papers.

In 2007, the producers started cutting out the show's soundtrack and using different musicians to re-record new music for the past-season highlights show "American Idol Rewind," the lawsuit said.

The union was not informed of the recording, according to court papers.

Phone messages left Thursday night with a representative for American Idol Productions were not returned.