The New Democrats are demanding that the federal government ensure all senators “are actually qualified to sit in the Senate” as the expenses scandal continues to plague the chamber of sober second thought.

NDP ethics critic Charlie Angus told reporters Friday that he has written to Pierre Poilievre, the Conservative government’s newly minted minister for democratic reform, to explain what action he intends to take to ensure all senators are “respecting the rules.”

“The Senate is facing an unprecedented credibility crisis with Canadians,” Angus told an Ottawa news conference.

“And if the Senate and the government are unwilling to address whether or not Senate appointees are even eligible to sit in the senate, this will only further erode confidence in this institution and it will also further erode confidence in this prime minister who promised Canadians that he would establish transparent and accountable government.”

Under the constitution, senators must live in the province they represent in the Upper Chamber, and recent audits into housing and travel expenses of a handful of senators have raised questions about whether they meet the residency requirements.

Outside audits of Senators Mac Harb, Patrick Brazeau, Mike Duffy and Pamela Wallin uncovered nearly $500,000 in improperly claimed expenses and raised questions about their primary residences. All four audits have been referred to the RCMP.

On Thursday, Auditor General Michael Ferguson also confirmed that he will review the expenses of all senators.

Last December, the Senate announced it was conducting an internal audit of each senator’s primary residence.

In February, Prime Minister Stephen Harper told the House of Commons that all senators conform to the residency requirements. “This is the basis to which they are appointed to the Senate,” he said.

However, Angus disputed that claim, because Wallin could only provide one of four required pieces of proof of residency in Saskatchewan, the province she represents: a driver’s licence. The outside audit, conducted by Deloitte, also concluded Wallin spent more of her time at her home in Toronto.

“So we are asking the democratic reform minister for this government to take this issue seriously to come out and say a clear declaration: are they going to deal with senators who do not meet the residency requirements, and what are they going to do about it?” Angus said.

The NDP MP wants Poilievre and the prime minister to “come clean” about what concerns, if any, were raised during the vetting process before the senators now caught up in the scandal were appointed.

“We would like to know, did the Privy Council do a proper vetting, did they give advice to the prime minister and if the prime minister received that advice, did he choose to ignore it?” Angus said.

“Because I think this is the fundamental legitimation crisis that the Senate is facing.”