Talk show host Jay Leno has come under fire from the Writers Guild Of America (WGA) for writing his own jokes for the comeback edition of his programme.
Jay Leno has been supporting the strike action
The union said in a statement he had "violated" their strike rules, despite Leno's insistence it was allowed as part of his agreement with the union.
Leno returned to US screens without his regular team of writers due to the strike, which began on 5 November.
Writers have been lobbying to win pay for material used on DVD and online.
The WGA has declined to comment on whether it will take any further disciplinary action with guild member Leno, which could include a fine or loss of membership.
TV network NBC, which airs the chat show, said Leno is permitted to write his own comic monologue.
During his show, the first after a nine-week hiatus due to industrial action, Leno told the audience that he was allowed to use material written without the help of outside writers.
"We are following the guild thing. We can write for ourselves," he said.
But on Thursday's edition he made no reference to the dispute, while his publicist declined to make any comment on the matter, saying Leno was busy with show preparations.
Leno has publicly supported the WGA action, delivering doughnuts to the picket line and paying the salaries of other employees on his show hit by the strike.
His return show on Wednesday night drew 7.2 million viewers, while rival David Letterman on CBS attracted an audience of 5.5 million.