The ethics watchdog overseeing Ontario's MPPs says he can't investigate a former Liberal Party staffer's claim that a then-member of the legislature sexually harassed and touched her inappropriately.

The female staffer alleges that the Liberal MPP touched her chest and thigh, stood with his crotch too close to her face, made crude sexual gestures and sounds, and sent suggestive emails.

The incidents are alleged to have happened in 2006 during Dalton McGuinty's time as premier.

The staffer claims that senior officials working for the Liberal Party at Queen's Park at the time failed to address the MPP's behaviour when she raised it. The woman claims that she was fired because of her complaints.

CBC News does not know the names of either the staffer, the MPP or the Liberal officials.

The allegations are laid out in a letter from Integrity Commissioner David Wake to the woman's lawyer, John Nunziata, in which the commissioner declines to investigate the case. Nunziata provided CBC News with a copy of the letter with the names of his client, the MPP and the senior Liberal officials blacked out.

In the letter, Wake says he cannot proceed with the sexual harassment claim because the legislation that governs his role does not give him the scope to investigate the former MPP.

David Wake, Ontario's integrity commissioner, is responsible for monitoring MPPs' compliance with the province's ethics laws. (Mike Crawley/CBC)

"While the allegations describe behaviour that could be potential wrongdoing ... I would have no jurisdiction to summons or otherwise obtain information from (the ex-MPP) during the course of an investigation," writes Wake in the letter dated Oct. 12.

The commissioner also says he cannot look into the allegation that the Liberal party officials failed to address the woman's complaints.

"The individuals you named were not public servants at the time of the alleged wrongdoing; they were employees of the Liberal Caucus Service Bureau. Accordingly, I do not have jurisdiction to accept this allegation against them," writes Wake.

"He's not passing judgment on the validity of the allegations, he's saying he can't investigate," Nunziata said Wednesday in an interview.

In February, then-premier Kathleen Wynne confirmed to reporters that her office had received information about the case. She described it as "troubling allegations related to an MPP who held a cabinet office portfolio at one point, left the legislature many years ago and was never a member of my or [former] premier [Dalton] McGuinty's cabinet."

Wynne's description would indicate the MPP had been in David Peterson's cabinet in the late 1980s.

John Nunziata, a lawyer and former Liberal member of Parliament, is representing the woman in the case.

Also in February, the Liberal Party offered to investigate, but Nunziata said his client wanted an independent probe, so took her complaint to the integrity commissioner.

Nunziata said he will ask Premier Doug Ford to change provincial law to give the integrity commissioner the power to investigate sexual harassment allegations involving political staff at Queen's Park. Such cases have long been handled internally by the political parties.

"The party caucuses at present basically govern themselves," said Nunziata.

"In this particular case, there was a reason why they would want to sweep it under the carpet," he said. "It would have made the government look bad. Individuals in the premier's office at the time, they listened to the allegations but at the end of the day they did nothing."

The integrity commissioner's office declined comment.

"We generally do not comment on whether or not the Commissioner is reviewing or investigating a matter," said Michelle Renaud, a senior policy adviser to Wake, in an email to CBC News.