The leader of the opposition in the Senate is suggesting that Prime Minister Stephen Harper's office may have violated parliamentary privilege, and could be in contempt as a result.

Liberal Senator James Cowan is asking the Speaker of the Senate to find the government in contempt over the fact Prime Minister Stephen Harper's former chief of staff, Nigel Wright, gave Sen. Mike Duffy over $90,000 to repay improperly filed housing expenses.

CTV's Ottawa Bureau Chief Bob Fife reported recently that a draft report into Duffy's activities included harsher language than the final report, which was issued after he had repaid the claims with the money given to him by Wright.

Cowan said it's important that Canadians find out exactly what happened and who was involved.

"When a payment is made to a senator by someone who occupies the position of chief of staff to the prime minister and there are suggestions made by Mr. Duffy that if he made the repayment the Senate would go easy on him, what does that mean and is there any connection between that phrase 'going easy' on him and the fact the senate report, internal economy report on him, was sanitized and was a whitewash," Cowan told reporters Tuesday evening.

Cowan said he'd like to see special parliamentary hearings held in Senate to get to the bottom of the controversy. If Senate speaker Noel Kinsella agrees, he could send the issue to a special committee. That could result in Wright, Duffy, and even Harper being called to testify, he said.

If there is a connection, he said, and if the payment to Duffy influenced the decision of a Senate committee, "then that is contempt of Parliament and that infringes on my privilege as a senator."

The Conservatives, who have a majority in the Senate, moved Tuesday night in a debate to have the audit of Duffy's expenses returned to the closed-door internal economy committee. Cowan and the Liberals had wanted that audit referred to police.

Cowan also asked Sen. Marjory LeBreton, the government leader in the Senate, to clarify why the report on Duffy's claims was "whitewashed" in comparison to similar reports on spending by Sen. Mac Harb and Sen. Patrick Brazeau, which included tougher language.

According to The Canadian Press, LeBreton suggested it was because Duffy had already paid his expenses -- a move which the government at the time said demonstrated "leadership" and should serve as an example to Brazeau and Harb.

Also Tuesday, Ethics Commissioner Mary Dawson confirmed her office had launched an investigation into Wright’s cheque to Duffy under the Conflict of Interest Act.

“The Commissioner and her Office cannot comment on the examination, as all examinations are conducted in private,” Dawson’s office said in a statement.

Wright resigned Sunday, while Duffy quit the Conservative caucus on Thursday. Another Conservative-appointed senator facing an expenses audit, Pamela Wallin, recused herself from the Conservative caucus on Friday.

NDP Leader Thomas Mulcair said Wednesday the latest controversy serves as "proof" the Senate needs to be abolished. He unveiled an NDP campaign asking Canadians to sign a petition to that effect, complete with a website with the slogan "Roll Up the Red Carpet."

"We're going to stop trying to find excuses for keeping a bunch of party hacks, bag men, political operatives and defeated canditates sitting in appeal of the decisions of the duly elected members of the House of Commons. That's over, that's a game of the past, it's a mug's game," Mulcair said in Ottawa,

On Monday, sources told Fife that Harper’s former special counsel and legal adviser Benjamin Perrin helped draft a letter of understanding that called for Duffy to publicly declare that he would repay the money. In return, sources said, Wright would give a personal cheque to Duffy to cover the $90,000. Sources also said the agreement stipulated that a Senate investigation into expense claims would go easy on Duffy.

On Tuesday, Perrin said in a statement he was “not consulted on, and did not participate in, Nigel Wright’s decision to write a personal cheque to reimburse Senator Duffy’s expenses.”

“I have never communicated with the Prime Minister on this matter,” he added.

Meanwhile, Harper departed Tuesday afternoon for Peru, where he is holding bilateral trade discussions before heading to Colombia for talks on the Pacific Alliance trade group. Chile, Colombia, Mexico and Peru are permanent members of the trade group, while Canada has observer status.

However, Canada already has free-trade agreements with all four countries and critics have questioned the timing of the out-of-country trip with so much going on in Ottawa.