A Senate committee has ordered Senator Mac Harb to repay $51,000 within 30 days, and has given him the option to repay a total of $231,649 if he does not want to face an extended and detailed audit of his expenses dating back to at least 2005, CBC News has learned.

The information comes from a copy of a letter from the Senate internal economy committee that's dated June 3. The $51,000 was included in a Senate report released on May 9, after an outside audit conducted by the accounting firm Deloitte gave its findings about how much time Harb spent in the house he called his primary residence near Pembroke, Ont., during an 18-month period.

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Since then, Senate staff has looked at the amount Harb charged for maintaining a secondary residence in Ottawa dating back to 2005, and has calculated he owes a total of $231,649 for mileage and living expenses, including interest. The total includes the $51,000.

Exclusive: Pamela Wallin breaks her silence CBC News Chief Correspondent Peter Mansbridge has an exclusive interview with Senator Pamela Wallin on The National. She talks at length and in detail about the scandal rocking the Senate and her own travel expenses. Watch The National's interview with Senator Pamela Wallin.

In a May 9 meeting, the 15-member Senate committee that monitors senators' expenses reported it does not believe Harb's Pembroke home is actually his primary residence.

Senators are allowed to charge living and travel expenses if their primary residence is at least 100 kilometres from Ottawa.

On Thursday, during a meeting of the internal economy committee, Senate finance staff who were present made it clear they had not done a "review" of Harb's expenses, but that the $231,000 was a ''calculation." It appears Harb is being offered a choice — to agree to repay a final figure of $231,000, or auditors will be called in to do a far more complex investigation.

Harb and Senator Patrick Brazeau have been asked to repay within 30 days thousands of dollars that the Senate says they owe for improperly claimed housing allowances, while the highly anticipated audit on Senator Pamela Wallin is expected to be completed next month.

Committee opens doors

The Senate's internal economy committee heard these revelations at a Thursday morning meeting opened up partly to the media. The committee normally holds closed meetings, but reporters were allowed in for some of the proceedings.

The committee chair, Senator David Tkachuk, told the committee he sent letters to Brazeau and Harb with the new deadline. Brazeau's letter was sent May 28 and he is to repay $48,745.13 for housing and mileage expenses. The letter to Harb asking him to repay $231,649.07, and hand over $51,000 of that amount within 30 days, was sent June 3.

An unidentified man shields Senator Pamela Wallin from media cameras as she arrives at the Senate entrance last week. (Sean Kilpatrick/Canadian Press)

Senator Carolyn Stewart Olsen said after the meeting that if the senators don't pay within the 30 days, the Senate has options to get the money back and she mentioned offsetting their salaries.

The committee also heard that the cheque that paid the government back for Senator Mike Duffy's expenses was drawn from a Prince Edward Island bank account. But later a member of Senate staff contacted Senator Percy Downe and told him the cheque was drawn, in fact, from an Ottawa bank, and not a P.E.I. bank, as had been mistakenly reported to the committee. But, the staffer said in an email to Downe, Duffy's P.E.I. address was on the cheque.

Duffy, a P.E.I. senator, paid back about $90,000 for expenses, but the money came from Prime Minister Stephen Harper's former chief of staff, Nigel Wright, who wrote a personal cheque to Duffy.

Auditors from Deloitte, the firm hired to look at the housing and travel claims of Brazeau, Duffy, Harb and Wallin, were at the committee meeting and said they expect to be finished with Wallin's audit by the end of July. The audits and Senate reports on the other three senators were released in May.

Tkachuk said outside the committee meeting Wallin "may not owe anything," but confirmed she has repaid $38,000 on her own volition.

The Deloitte auditors told the committee they had intended to finish the Wallin audit by the end of June, but have been delayed because they're waiting for information from a "third party."

Tkachuk told reporters there may be more than one third party, but said he doesn't know who they are. He said, for example, Deloitte might need to contact an organizer of a meeting Wallin claimed she attended to determine if she was really there.

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The Deloitte staff said they are examining Wallin's claims dating back to when she was first appointed as a senator for Saskatchewan in January 2009, a longer period than they were originally asked to examine. They said they are examining the nature of her expenses, trying to determine whether she was on Senate business when she made expense claims.

Wallin report expected end of July

They said they expect to be finished their work by mid-July, then their report will have to be translated and is expected to be finished at the end of the month.

The Senate is scheduled to sit until June 28 and reports traditionally are not tabled when Parliament is not sitting. The House of Commons and the Senate are scheduled to resume sitting Sept.16.

The internal economy committee might pass a motion Thursday that would permit a report to be tabled with the Senate clerk when the chamber is not in session.

The Senate report that accompanied the audit on Harb ordered him to repay $51,000 in housing and living expenses claimed over 18 months from April 2011 to September 2012, but also recommended that a review going back further in time should be done.

Senator Elizabeth Marshall confirmed to the committee that Senate audit staff were the ones who did the deeper review, not Deloitte, and came up with the higher figure of $231,649.07.

CBC News was told that new figure on Wednesday and that the review period dates back to 2005-2006. Harb was appointed in 2003.

Harb has hired legal counsel and is challenging the audit findings. His lawyer, retired Supreme Court justice Michel Bastarache, said Wednesday that his client would be making a statement within a few days.

The Senate report in May said Brazeau had to repay $48,000, but he is also challenging the findings.

A spokeswoman for Brazeau, Debby Simms, told CBC in an email on Thursday that his office has complied with Senate policy and that "given the inordinate amount of political manipulation around the process, we believe that it is best left to the RCMP and the Auditor General to determine the facts regarding Senator Brazeau's expense claims."

"With so many closed-door meetings, political interests, and grandstanding from all sides, the very credibility of the board of internal economy is in question," she wrote.

In other news, the Senate's internal economy committee chose a new chair on Thursday, Senator Gerald Comeau, to replace David Tkachuk. Tkachuk said earlier in the week that he has to undergo treatment for bladder cancer and could not carry out his committee duties.