OTTAWA - Two leading Conservative senators say the red chamber may need to tighten its rules for expense claims following the scandal that plagued it over the last three years.

Senate Conservative Leader Claude Carignan and Sen. Denise Batters, who sits on the internal economy committee that sets spending rules, say changes are possible to how senators claim their expenses.

But Carignan said any changes will require the leadership of the Senate government leader.

"I don't know if we need to change, [but] we probably have to review and establish maybe another system to determine the intention of each senator to establish his main residence in his province," Carignan told CTV News in Ottawa.

"But we have to also work with the leader of the government... It's impossible to change those type of rules without the agreement of the leader of the government. So we will see in the future, but we work very strongly to rebuild the confidence of Canadians in the Senate and I hope that those type of issues will not delay our work to rebuild confidence."

Carignan is a former government leader in the Senate under the Conservatives.

The current rules allow for senators whose primary residence is outside the Ottawa-Gatineau area to claim expenses worth up to around $22,000 a year when they're working in the capital. The Senate scandal was triggered when senators who had lived in Ottawa for decades prior to being appointed were reported to be claiming those expenses. Mike Duffy, who had been a journalist in Ottawa since the 1970s, and Mac Harb, who was an Ottawa city councillor and then a long-serving MP representing Ottawa Centre, were charged with fraud and breach of trust. Patrick Brazeau, who had also worked in Ottawa prior to his appointment, was also charged in relation to his housing claims – though not for per diems - and Pamela Wallin was investigated over her travel expenses. Duffy was found not guilty on all 31 charges, and the Crown dropped the charges against Harb and Brazeau in the wake of the Duffy decision. The RCMP closed its investigation into Wallin without recommending charges.

Harb retired from the Senate in 2013. Duffy, Brazeau and Wallin were suspended until the election call last summer, with Duffy returning to his duties following his trial (Wallin returned to work after the election and Brazeau after his charges were dropped). Since his return last spring, Duffy has claimed $1,691. The new expense claims suggest Duffy meets the eligibility requirements set out in 2013 that show his primary residence is in Prince Edward Island, the province from which he was appointed.

Batters said the Senate has already implemented changes, including the proof of residency, which requires a provincial health card and driver's licence, as well as a federal notice of tax assessment.

"We're constantly reviewing our rules and procedures and making sure that it remains the efficient, transparent and accountable process and institution that Canadians deserve and expect," Batters said.

"We always are considering additional rule changes, yes."

Carignan pointed out there are two sets of rules senators need to follow - the criteria that allow them to be appointed, which are set out in the Constitution, and the administrative rules that govern how they do their jobs.

"What we could change or review on our side, it's the administrative rules," he said.

Peter Harder, the non-partisan senator appointed by Prime Minister Justin Trudeau to be the Senate government leader, wasn't available for an interview due to travel.