Prime Minister Justin Trudeau must put pressure on the Senate to strengthen its disciplinary rules in the wake of a damning report about Senator Don Meredith and his sexual relationship with a teenager, the NDP's democratic reform critic says.

In a letter written to the prime minister Wednesday, Nathan Cullen said it is unconscionable that a senator could stay on as a member of the Red Chamber after engaging in this type of behaviour.

"While voters can give the proverbial boot to governments with whom they have lost faith, Canadians have no ability to dismiss their representatives in the Senate. It's time the Senate implement new rules for the removal of senators who have violated ethical standards," Cullen wrote.

Bad behaviour is inherent in a place where there is no accountability. - NDP MP Nathan Cullen

The B.C. NDP MP said nothing less than expulsion will suffice. "If not for this, then what? Did she need to be 14 or 15?" he said in an interview with CBC News. In any other workplace, Meredith would be fired, Cullen said, "The Senate's solution is to send him to a women's conference."

"Senators sit with the firm knowledge that they are untouchable; they have taken money, they have physically assaulted people, and they have conducted themselves in unethical ways for over a century," Cullen said. "It becomes slightly less awful in terms of democratic values if they're at least a little bit more accountable to themselves."

Lyse Ricard, the Senate's ethics officer, found that Meredith violated two sections of the code of ethics, namely that the Toronto-area senator and Pentecostal pastor did not uphold the highest standards of dignity inherent to his position, and that his actions reflect adversely on the institution of the Senate.

Meredith denies many of the allegations levelled against him by the woman in question — who is identified as "Ms. M" in the report — but concedes he had sexual intercourse with her on at least one occasion. Ottawa police investigated the matter but dropped the case without pressing criminal charges.

Senator Don Meredith has been referred to the ethics officer after a report of an alleged inappropriate sexual affair with a young woman, which prompted his removal from the Conservative caucus. (CBC)

Ricard found reason to believe Meredith and Ms. M had intercourse three times, including once when the woman was 17 years old. Meredith denies the allegation. Her report has now been sent to the Senate's ethics committee for review, leaving senators to decide on an appropriate course of action.

The Constitution Act, 1867 enumerates five areas regarding when a senator can be permanently disqualified, but the document does not specifically address a case like the one currently before the Senate, where the prospect of a criminal conviction is unlikely.

"Bad behaviour is inherent in a place where there is no accountability. You and I know both know Senator Meredith won't be the last one. They're unelected, unaccountable and often under investigation," Cullen said.

Senate has power to expel: expert

While Cullen is calling on Trudeau to take action, some in the Red Chamber aren't waiting for his intervention and are already mobilizing to remove Meredith. As CBC News first reported Tuesday, the chamber's law clerk has been tasked with preparing possible legal avenues for expulsion.

The clerk, and other constitutional experts, has pointed to Section 18 of the Constitution, which stipulates that Canadian parliamentarians should have the same privileges as a British MP. Members of the British House of Commons have the power to expel one of their own, and have used it sparingly to eject wayward MPs.

'I think it's clear that Senate has those privileges,' says constitutional lawyer Marc-Andre Roy. 6:01

"The Senate has all the powers that are necessary to protect its integrity and to assure its proper functioning, and that includes the power to discipline senators, and it can go all the way up to expelling members," Marc-André Roy, a constitutional law expert who spent several years working for the Senate, said in an interview.

"The Senate is certainly free to vote on the matter. They have rules in place, they have an internal process," he said.

Trudeau distancing himself from Senate

Trudeau has sought to distance himself from the Senate, kicking Liberal senators out of the national caucus, and establishing an independent advisory board to make recommendations on senatorial appointments.

"I think this is a question for Senate leadership as they continue to move forward in demonstrating the effectiveness and value of an upper house," Trudeau said last week when asked about ethics report.

"It is not for me to weigh in on how the Senate should continue to conduct itself, but of course every politician in Canada, senator or MP … needs to conduct themselves in a way that is worthy of the public trust placed in them."

Cullen said this answer from Trudeau is nothing but a cop-out. "He's still the prime minister, he's still the one who puts people into the Senate virtually for life. He can't just say, 'I'm satisfied with the way things are,' because as long as he keeps appointing people, he sees it as a legitimate place. He must lift a finger to make it more accountable and respectful."

Peter Harder, Trudeau's representative in the Senate, is responsible for leading reform efforts and realigning the chamber along nonpartisan lines. He has publicly called on Meredith to resign, and has mused about the possibility of expulsion.