The NDP will be asked Tuesday to repay money spent to send out flyers touting Tom Mulcair's leadership during a Montreal byelection last year, CBC News has learned.

Multiple sources say the powerful and secretive Board of Internal Economy (BOIE), which includes MPs from all parties in the Commons, has ruled the New Democrats broke House rules by using parliamentary resources to distribute leaflets in the Montreal riding of Bourassa. The board may also direct House administration officials to review other NDP mailings as well.

The Speaker's office is expected to issue a written statement on its findings on Tuesday morning.

That could potentially leave the party — or, to be specific, individual MPs — on the hook for tens of thousands of dollars.

Although the NDP wasn't prepared to confirm the repayment order, a party official told CBC News that "the old parties" were "ganging up against the NDP behind closed doors."

"No due process, no rule of law and foregone conclusions from a secretive body now used as a political attack machine," the official said.

On Monday evening, the party issued a written statement defending the "outreach program" and accusing the Liberals and Conservatives of turning the Board of Internal Economy​ into a "kangaroo court."

"We conducted extensive consultations with the House of Commons and the Speaker to confirm that this program respected all applicable rules," it noted.

"In the face of the evidence, it would have been only logical for the BOIE to do the same. Instead, a majority of its members opted today to openly hijack our democratic institutions."

The party's spending practices have also been in the spotlight at the House procedure committee.

Last month, MPs got the chance to question Mulcair on both the pre-byelection mailings and the party's now closed satellite offices in Toronto and Quebec, which were staffed by employees paid out of the House budget.

Speaker told MPs he wasn't consulted on mailings

Under questioning, Mulcair was adamant that his party had followed the rules.

Earlier this spring, he told reporters they had "checked and double-checked" with House of Commons Speaker Andrew Scheer "before going that route."

But last week, Scheer told the committee that his office wasn't consulted on the Bourassa mailing at all, which seemed to contradict Mulcair's earlier assertion.

For its part, the NDP pointed to an April 2013 letter sent to Scheer's office by party whip Nycole Turmel, who wanted clarification on the mailing rules.

In a written statement issued after his testimony, Scheer acknowledged the correspondence, but said he stood by his answer.

That apparent inconsistency was enough to prompt some committee members to muse openly about recalling Mulcair to the witness stand.

On Friday, a spokesperson for Mulcair told CBC News that he has no intention of submitting to a second round of questioning.

The NDP has also asked Scheer to rule on the motion that originally triggered the committee investigation, which it says should have been ruled out of order on procedural grounds.