WGA says naughty, naughty; Leno says, “Not.”

The WGA’s told Jay Leno that he can’t write jokes without breaking the guild’s strike rules.

Move came Thursday afternoon after Leno delivered a self-written monologue in his return to the air on Wednesday night. And that’s a no-no since Leno’s working for a struck company, according to the WGA strike rules.

“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 Guilds’ strike rules,” the WGA said in a statement.

The guild did not elaborate further.

Under the strike rules, Leno could be punished via expulsion, suspension, fines and censure – although a hardline response might backfire in terms of generating sympathy for Leno.

Leno said during his opening that he believed he was following WGA rules.

“I write jokes and wake my wife up in the middle of the night and say, ‘Honey, is this funny?’ So if this monologue doesn’t work it’s my wife’s fault,” he said. “We are not using outside guys. We are following the Guild thing. We can write for ourselves.”

— Dave McNary