"Tonight Show" host Jay Leno's on-air declaration that he wrote his own jokes for his program triggered a thorny dispute Thursday about what the late-night hosts can and can't do during the continuing writers strike.

Leno's statement that he penned his monologue put the popular comedian at odds with his own union despite his vocal support for its cause.

"I'm doing what I did the day I started," Leno said Wednesday night during his first show since Hollywood writers walked off the job in November. "I write jokes and wake my wife up in the middle of the night and say, 'Honey, is this funny?' "

The NBC comedian assured his audience that he was following the rules set by the Writers Guild of America.

"We are not using outside guys," he added. "We are following the guild thing. We can write for ourselves."

But Leno's explanation runs contrary to the guild's own strike rules, which say WGA members cannot perform writing services for struck productions.

On behalf of Leno, NBC defended his decision, saying that he is allowed to write for himself and questioning the authority of the guild's regulations. The host wrote his monologue again Thursday and plans to continue doing so, the network said.

The dispute led the comedian Thursday to call Patric Verrone, president of the Writers Guild of America, West, to explain why he believes he can write material for himself, according to an NBC executive.

Leno's stance creates an awkward dilemma for the guild, which must decide whether to take a position against one of its most prominent members or risk angering rank-and-file writers who believe the union has to maintain a united front.

Guild members who violate strike rules can be subject to disciplinary action by the WGA, including financial penalties and expulsion. But the WGA does not plan to take disciplinary action against Leno, according to a senior guild official who asked not to be identified because of the sensitivity of the matter.

On Thursday, after declining to speak in detail on the matter, the guild released a guarded statement.

"A discussion took place today between Jay Leno and the writers guild to clarify to him that writing for 'The Tonight Show' constitutes a violation of the guild's strike rules," it read.

Muddying the issue are conflicting sets of regulations.

WGA officials warned in recent weeks that the union's strike rules prohibited the late-night hosts from writing material if they crossed the picket line to return to their shows.

The main reason: The monologues and other features on the programs are usually penned by guild writers -- at least in part -- and are thus considered "struck work." On top of that, since the hosts are guild members and credited as writers on the shows, they are prohibited from writing.

"If they are employed as writers on the show, the rule as we see it is they are barred from performing writing services," Tony Segall, general counsel for WGA West, said during an interview in December. "They cannot write their own material. We would view that as a violation."

NBC attorneys say the union's position goes against its own collective bargaining agreement with the studios. In that agreement, the definition of what writing is considered union work specifically excludes "material written by the person who delivers it on the air" on variety shows. Although the WGA contract expired Oct. 31, its provisions still apply, network lawyers said.

In addition, the contract states that neither party is allowed to adopt regulations that conflict with the agreement, which the guild's strike rules do, NBC asserted.

"The WGA agreement permits Jay to write his own monologue," said Andrea Hartman, NBC's deputy general counsel. "The strike rules can't contradict the scope and expressed terms of the basic agreement."