The Conservatives took advantage of the fact that the NDP had fewer than 25 MPs in the House of Commons early Thursday to force a snap vote on a motion from Tory MP Blake Richards.
Richards' motion requires Mulcair to appear before the procedure and House affairs committee to answer questions about the NDP's use of parliamentary resources to staff satellite party offices in Quebec and Saskatchewan.
He'll also be grilled about New Democrat MPs using their free parliamentary mailing privileges to distribute partisan flyers in four ridings as they did in the midst of byelection campaigns last fall.
New Democrats insist Mulcair has nothing to hide and is happy to testify before the committee.
And they're countering with a motion of their own, asking that Prime Minister Stephen Harper also be invited to committee to explain the Conservative party's use of government resources to fund partisan activities.
"We just thought we'd return the favour," said NDP MP David Christopherson, who moved the counter-motion at committee.
"The government seems to want to focus on this. Fine, then let's do it, let's bring in the prime minister and have at 'er."
He charged that the Tories are simply trying to create a diversion so that the committee, which is studying the government's proposed overhaul of election laws, will have less time to hear expert witnesses trash the bill.
The NDP's counter-motion was not put to an immediate vote.
Conservative, Liberal and Bloc Quebecois MPs have complained that the NDP is using taxpayer-funded, parliamentary resources for purely partisan activities, which are supposed to be funded by political parties.
In particular, they've complained about partisan flyers mailed by New Democrat MPs to households in Toronto Centre, the Montreal riding of Bourassa and the Manitoba ridings of Provencher and Brandon-Souris during byelection campaigns last fall.
Earlier this week, the all-party board of internal economy, which oversees financial management of the House of Commons, asked Elections Canada to examine whether the cost of the mailings in the first three ridings should count towards the NDP's spending limit in the byelections.
It's not clear why the board didn't ask the watchdog agency to examine the cost of flyers distributed in Brandon-Souris, although Conservatives have complained about them as well.
As well, the board is doing its own review of bulk mailings by MPs to ridings other than their own.
Mulcair has said the flyers were mailed before the byelections were actually called, and were therefore entirely within the rules. He concedes some may have arrived in mailboxes after the call.
The internal economy board is also considering a Liberal complaint about the NDP setting up offices in Quebec and Saskatchewan, staffed with people on the parliamentary payroll.
Mulcair has said the Quebec office is intended to help the NDP's MPs in the province conduct outreach with their constituents.
He has not explained why a similar office would be needed in Saskatchewan, where the NDP has no MPs.