A senator who once headed the Conservative party's national council says he cannot support a motion by his leader to suspend three senators over their improper expenses because to do so would deny those senators their fundamental rights to justice and the rule of law.

Don Plett, a Conservative senator from Manitoba who is known as a staunch Conservative loyalist, stood in the Red Chamber to say the past week, when the Senate has been debating proposals to suspend Pamela Wallin, Mike Duffy and Patrick Brazeau, has been one of the most difficult of his life.

Mr. Plett said that, for the first time ever, he is considering voting against his leader.

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The Senate debate has raised questions about how involved Prime Minister Stephen Harper and his office may have been in the unfolding expenses scandal, in which four senators, including one former Liberal, have repaid tens of thousands of dollars in questionable expenses.

Although Mr. Plett said he had great respect for Claude Carignan, the Leader of the Conservative Government in the Senate, he said it would be wrong to over-simplify a complex issue at the expense of three senators whose lives would be greatly affected if they were indefinitely deprived of their jobs, their salaries and their benefits.

"We will be stripping them of everything except the title senator" said Mr. Plett. "Just because it is within our rights, doesn't mean it is the right thing to do."

Mr. Plett said the motion is incompatible with the presumption of innocence until guilt is proven. Although the expenses of all three senators are being investigated by the RCMP, none has been charged.

"All of a sudden, we are going to find them guilty and apply sanctions before we have let the police do their work," said Mr. Plett. "Now we are putting any chance of a fair investigation or future trials in serious jeopardy."

James Cowan, the Leader of the Liberals in the Senate, has introduced a motion to send the matter to the Senate's rules committee. But Mr. Plett said he was concerned that the committee's members are partisans thus open to accusations of bias. So unless the amendment is amended to send the issue to an independent body and to impose timelines, he said, he will probably not support it.

But neither, he said, will he support Mr. Carignan, whom he thanked for allowing senators to vote according to their conscience.

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"The only correspondence I have received from Canadians since this motion was introduced," said Mr. Plett, "is to respect the rule of law and not let politics get in the way of doing the right thing."

Veteran Conservative Senator Jean Claude Nolin said that, although he respects the right to due process, the Senate is not a criminal court and senators have the right to exercise their power over their own House.

His Conservative colleague, Hugh Segal, who opposes Mr. Carignan's motion, said he is not quibbling with the right to discipline its own members but, if the Senate goes down that route, there are rules to be followed. "We are trying to commit professional capital punishment on three of our members," said Mr. Segal.

Senators on all sides of the chamber gave Mr. Plett a loud round of applause and the Liberal senators gave him a standing ovation. But few Conservative senators are expected to join him in voting against Mr. Carignan's motion.

Mr. Plett's address was followed by a statement from Majory LeBreton, the former leader of the government in the Senate, who tried to rip holes in the story that Mr. Duffy told in the Senate earlier this week. Mr. Duffy said he was forced to pay back $90,000, even though he did not believe it was owed, to appease the Conservative government which was taking a hit in the media and from its party members over the issue.

"The story that Sen. Duffy spun in this place was not based in fact and it certainly leaves open the question what he was talking about and what he was thinking," said Ms. LeBreton. Mr. Duffy had an opportunity to explain in the Senate why he thought his expenses were appropriate, said Ms. LeBreton. "He did not."

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Ms. Wallin and Mr. Duffy told fellow Senators this week during a debate on their possible suspensions that they were victims of a conspiracy orchestrated by the Conservatives to remove them from their jobs because they had become political liabilities – and both cast Ms. LeBreton as a key player in the government's scheme. She was the Conservatives' Senate leader from 2006 until this summer.

As for Mr. Duffy, Ms. LeBreton said in an interview she has kept rigorous notes and his story does not hold up.

Mr. Duffy said Tuesday that he repaid $90,000 in expenses only because he was pressured by Conservative senators and the Prime Minister's Office to do so – under threat of losing his seat. Nigel Wright, the Prime Minister's then-chief of staff, later admitted that he gave $90,000 to Mr. Duffy to cover the repayment and he resigned.

Mr. Duffy said he met privately with Mr. Harper and Mr. Wright – "just the three of us" – after a caucus meeting on Feb. 13 where he insisted that he had not broken any rules.

Ms. LeBreton said she has searched her files and found no trace of a two-page memo sanctioning Mr. Duffy's expenses. And she was forced to remove him from caucus after a string of improprieties had been made public in one painful revelation after another.

"We had a very upset Senate caucus and obviously a very concerned elected House of Commons caucus," she said.

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"So when Ray (Novak, Mr. Harper's chief of staff) and I called Mike Duffy, it was a very nice conversation. We told Mike that we basically gave him two options to step aside voluntarily until all these matters were resolved and at that time we thought these matters could be resolved," she said. "But this idea that I said the deal was off – what deal was there to be off?"

Mr. Brazeau tabled a document in the Senate on Thursday that he says proves he was told he was eligible to claim resident expenses for an apartment in Ottawa.

In an e-mail that was dated in March, 2011, the Senate's finance officer said that, if a senator rented an apartment, he would have to submit a copy of his lease. She urged Mr. Brazeau's assistance to read over the guidelines for Senate expenses.

But the issue uncovered with Mr. Brazeau's expenses was not that he had an apartment in Ottawa but whether he actually spent time at his declared home in Maniwaki, Que. – and whether his primary residence was actually in Ottawa which would have disqualified him from reimbursement.