New Democrat Leader Tom Mulcair says the Liberals and Conservatives are using their majority on a secretive Commons committee to attack his party now that it rising in the polls.

The board of internal economy has confirmed that dozens of NDP MPs may soon find their expense claims being rejected by House administration as a result of their failure to repay $2.7 million that went to fund now-closeed NDP satellite offices in Montreal, Quebec City and Toronto.

Mulcair initially denied that the House was preparing to take action against individual MPs.

"That's false," Mulcair told reporters during an impromptu scrum outside the NDP caucus room Wednesday.

"It's just our Liberal and Conservative adversaries using their majority to try to frustrate the party that's coming up in the polls, and doing well compared to the two old-line parties."

But in a statement sent to CBC News, a spokeswoman for Conservative whip John Duncan said that starting July 1, the Commons will indeed start rejecting expense claims from NDP MPs who took part in the budget-pooling scheme.

"Administrators will collect the money by refusing to cover expense claims — per diems, travel expenses, etc," Christine Maydossian said. 

She added that there is "nothing preventing individual members from writing personal cheques." 

Later, a question about suspended senator Mike Duffy's own now-infamous expense repayment gave Prime Minister Stephen Harper his opening to counter-attack Mulcair during question period. 

"Canadians are wondering why the leader of the NDP continues to justify taking nearly $3 million in parliamentary funds and using it completely inappropriately, for partisan purposes, and not being willing to pay it back, and not being willing to apologize, and reverse course."

'Not a scintilla of evidence': Mulcair

The New Democrats have steadfastly denied breaking House spending rules by pooling contributions from MPs' office budgets to foot the bill for the offices, which they maintain operated entirely within allowable parameters, despite being located far from the parliamentary precinct.

But last February, the committee charged with overseeing MP and party spending concluded that 68 current and former New Democrat MPs — including Mulcair himself — had "inappropriately used parliamentary resources" on costs related to the out-of-town outposts, which included salaries, transport and telecommunications.

In a statement issued on behalf of the Board, House of Commons Speaker Andrew Scheer said that, as "individual Members' Office Budgets were used to supplement the NDP Research Office Budget," it would be up to "each participating member" to "personally reimburse" the money.

The MPs were given 90 days to comply with the request, but the March 31 deadline came and went with no further action until this week.

"There's never been the slightest indication — not a scintilla of evidence that the NDP didn't respect all the rules," Mulcair said on Wednesday.

"You know why? Because the NDP has respected all of the rules, every single step of the way. We have used our staff appropriately. And whenever they change the rules, we respect the new rules as well," he added.

"They know that."

"Obviously they've chosen to try and push on issues that they think will hurt us," NDP MP Carol Hughes told reporters on her way into Wednesday's caucus meeting. "They see us as quite the party to beat now."

"They're going to take punches at us because they don't like us moving up [in the polls]," NDP ethics critic Charlie Angus said. "We're just going to take a lot more punches before we get where we gotta go."

Neither Hughes nor Angus have been asked to repay money.

Trudeau slams Mulcair's leadership

Both Liberals and Conservatives denied that the issue resurfaced because of the NDP's buoyant popularity.

The misuse of funds, Liberal Leader Justin Trudeau told reporters after his own caucus met, has been going on for an awfully long time.

NDP Leader Tom Mulcair

NDP Leader Tom Mulcair denied to reporters Wednesday that his MPs were having difficulty getting their expenses reimbursed, as the squabble over paying back parliamentary funds used to run partisan satellite offices continues. (CBC News)

"What people expect from their leaders is when you make a mistake, you own up to it, you apologize for it and you make it right. You fix it," Trudeau said.

"Instead we see Mr. Mulcair trying to deny that anything actually happened and blame others. That's just not the leadership people need to see," the Liberal leader said.

"If you owe the money, you owe the money and that's what it looks like," Conservative MP Joe Preston told reporters.

Treasury Board President Tony Clement said that it was the Commons Speaker and a report from the House of Commons administration that found rules had been broken, not a partisan conspiracy.

Suggesting otherwise was "the argument of a group...who don't want to pay back the money they owe the taxpayers," Clement said.  

The New Democrats have challenged the board's finding in federal court. That case is expected to be heard later this year.

Meanwhile, despite the strong words from their leader, some New Democrat MPs are reportedly still worried.

And, as Maydossian pointed out, even the looming election won't necessarily get them off the hook. Even MPs who are no longer New Democrats or not running again must pay up.

"The dissolution of Parliament does not erase the requirement to repay improper expenses that were incurred during that Parliament," she noted.