Ontario Premier Kathleen Wynne has asked the leader of the Opposition to retract comments he made about her or face legal action.

The premier's lawyers wrote a letter to Patrick Brown on Wednesday, saying the Progressive Conservative leader had told reporters on Tuesday that Wynne was standing trial in a  Liberal bribery case. The letter said Wynne is not on trial or even under investigation, but is rather offering voluntary testimony and co-operating with the court process, therefore Brown should retract the comments and apologize.

Wynne's office made the letter public moments before the premier took the witness stand in a trial in Sudbury, Ont., for two former Liberal staffers who are facing bribery charges under the Election Act.

"She has gone so far as to waive her parliamentary privilege and will voluntarily appear as a witness at the trial, " wrote the premier's lawyer, Jack Siegel.

"There is a world of difference between this high level of co-operation and your defamatory reference to 'when she stands trial'; she is not on trial, and will continue to take all necessary measures to defend her reputation."

Brown was not available for comment. His office did not contest the leader's remarks, but pointed out that he immediately tried to clarify them when speaking to the media.

PC deputy leader Steve Clark said the Liberal government was trying to distract from the premier's testimony, which he called "an unprecedented situation".

"The government issued a press release before the premier testified," Clark said. "There will probably be other government announcements that will distract from the case. I'm not surprised."

Clark said the matter would be dealt with by lawyers from both sides.

This is the second time in a week that the Liberal government has threatened legal action over remarks made by a Progressive Conservative member of the provincial legislature  about the Sudbury trial. Last week, Bill Walker told a local radio station Wynne was under investigation and facing charges in connection with the bribery trial. Days later, he issued a statement apologizing for the remarks.

Deputy premier Deb Matthews denied suggestions that the government was trying to distract from the Sudbury trial.

"No, Patrick Brown is a lawyer," she said. "He knows that what he said was inappropriate. He knows he said it in a very, very public forum. I don't know why he didn't immediately correct the record."

McMaster University political science professor Henry Jacek said the lawsuit threat is basic political strategy, an attempt to correct the record immediately from the government. It's also not without precedent in politics but the cases rarely seem to actually go to court, he said.

"They want to get a message out to people that ... this is not true," Jacek said. "In this case, they decided that a lawsuit was the best way to do it. I see it more as political communication tactic than a legal tactic even though it is a legal instrument."