The Senate is auditing Sen. Pamela Wallin for hundreds of thousands of dollars in travel expenses over the past three years, CTV News has learned.

Expense records show the Conservative senator, who was appointed to the upper chamber in 2009, has claimed $321,037 in “other travel” expenses since September 2010.

She also spent $29,423 on flights from Ottawa to her home province of Saskatchewan.

A source told CTV News that about 70 per cent of Wallin’s flights were to Toronto, where she also owns a home.

Sources say Wallin, a former broadcaster, offered to pay some of the money back after she was questioned by a Senate committee. But insiders say the committee refused and hired accounting firm Deloitte to investigate her expenses.

Wallin denied that in an email to CTV News.

“I certainly did willingly meet with a representative from Deloitte to review travel expenses and I answered all questions and have provided all the necessary information regarding claims,” she wrote.

“No offer of repayment was made or asked for. I spent 168 days in Saskatchewan last year and most of my travel was to my home province.”

The Senate called in outside auditors to examine Wallin’s flight expenses in early January.

Last week, it was announced that Deloitte will audit the housing expenses of Senators Mike Duffy, Mac Harb and Patrick Brazeau. All three have denied any wrongdoing.

A $21,000 annual housing-and-meal allowance is offered to senators whose primary residence is more than 100 kilometres away from Ottawa.

Duffy, a Conservative senator who is also a former broadcaster, has claimed his primary residence is his home in Cavendish, P.E.I.  But he was not on the voters’ list there in 2011, and instead cast a ballot in Ontario’s provincial election that year.

Duffy’s office also tried to expedite an application for a P.E.I. health card so the senator would have it ahead of a Jan. 31 deadline for all senators to submit proof of their primary residence.

Brazeau has claimed that his primary residence is his father’s home in Maniwaki, Que., even though he rented a home in Gatineau, a short drive from Parliament Hill.

Brazeau has since been kicked out of the Conservative caucus and forced to take a leave of absence from the Senate, after being charged with assault and sexual assault.

Even though he has lost his Senate perks and can’t attend any sessions in the upper chamber, Brazeau will continue to collect his $132,000 salary while the case is before the courts.

Harb, a Liberal senator and a former MP, has also faced questions over expense claims for a secondary residence in Ottawa even though he has lived in the capital for many years. 

The Senate is now asking that all senators’ housing allowance claims be checked to determine their legitimacy.

The widening controversy surrounding senators’ expense claims dominated question period in the House of Commons Tuesday.

“Is the prime minister going to accept this corruption or is he going to hold his Senate cronies accountable for once?” NDP Leader Thomas Mulcair asked.

Prime Minister Stephen Harper responded by saying the Senate has “acted proactively and quickly to deal with the matters at hand.”

With a report from CTV’s Ottawa Bureau Chief Robert Fife