Senate leaders want all housing allowances checked to confirm their validity, as questions about claims made by three senators cast a shadow over the upper chamber.

The Senate’s internal economy committee is probing allegations that some senators have improperly claimed the $21,000annual meal-and-housing allowance, which is offered to those whose primary residence is more than 100 kilometres outside Ottawa and who must therefore find a secondary home in the capital.

The committee also called in accounting firm Deloitte to probe three specific cases concerning Conservative Sen. Mike Duffy, Liberal Sen. Mac Harb and Sen. Patrick Brazeau. All three have denied any wrongdoing.

On Monday, government Senate leader Marjory LeBreton and Liberal Senate leader James Cowan wrote to the committee to ask that all housing claims be vetted to ensure their legitimacy.

“We request that you proceed to interview each senator who has claimed a secondary residential allowance to confirm the legitimacy of such claims,” LeBreton and Cowan wrote. “Should any senator be unable to convince you that the claim is valid, that senator should be required to pay immediately all monies so paid with interest.”

In an interview Monday evening on CTV’s Power Play, Cowan said he and LeBreton “agree wholeheartedly” on the importance of getting to the bottom of the allegations.

“We have zero tolerance for anyone who is abusing the rules, and we think as a first step that they should pay the money back,” Cowan said. “We’re not presuming anything. We’re just saying we need to check this out and if money has been improperly claimed it should be paid back with interest, immediately.”

Cowan, who claims a housing allowance because his primary residence is in Nova Scotia, would not speculate on what should happen to any senator who is found to have made improper claims.

Duffy has claimed his primary residence is his home in Cavendish, P.E.I. However, he was not on the voters’ list in P.E.I. in 2011, and voted in that year’s provincial election in Ontario.

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

Harb, a former MP, is also a long-time Ottawa resident who has faced questions over expense claims for a secondary residence in the city.

Brazeau also denied wrongdoing after it was revealed that he had collected the housing allowance by listing his former father-in-law’s address in Maniwaki, Que., as his primary residence.

Last week, Brazeau was kicked out of the Conservative caucus after he was charged with assault and sexual assault following an incident at his home.

Cowan said he supports both the Senate committee’s probe into the housing allowance allegations, as well as the decision to call in an outside auditor. But he lamented the fact that the allegations and investigations undermine the upper chamber, which he admits is “an easy target.”

“This kind of thing is damaging to the institution,” Cowan said. “It’s easy to say someone’s alleged to have made improper claims therefore everyone is doing it. Well, my view is that most senators do the best they can, they work hard, and I think the institution does a lot of good work.”

With files from The Canadian Press