The NDP's complaint comes one day after the Liberals sought an investigation into New Democrat MPs' allegedly inappropriate use of their taxpayer-funded constituency offices to campaign for re-election.
Both complaints have been sent to House of Commons Speaker Andrew Scheer, who chairs the secretive, multi-party board of internal economy, which polices how Commons resources are spent.
In a letter Thursday to Scheer, Windsor NDP MP Brian Masse raises "serious concerns" about a Liberal caucus meeting on Parliament Hill last June, at which Trudeau showcased recently nominated candidates.
Masse says the event violated the rules, which forbid premises provided to an MP by the Commons to be used for partisan purposes.
However, deputy Liberal leader Ralph Goodale says that prohibition applies to individual MPs' offices; it does not apply to caucus meetings, which are inherently political and to which all parties, including the NDP, have routinely invited partisan operatives.
He noted that the NDP's national campaign director — who holds "probably the most intensely partisan position that any political party has" — regularly attends NDP caucus meetings.
In his letter Thursday to Scheer, Masse argues that the Liberal caucus meeting last June "does not appear to relate to the 'proceedings and work of the House of Commons' or the member for Papineau's (Trudeau's) constituents.
"Quite the opposite, the room was booked as a venue to showcase recently nominated candidates for the Liberal Party of Canada."
Within minutes of learning of Masse's complaint, Liberals were countering with photos tweeted from NDP caucus meetings. They showed, among other things, star Toronto candidate Linda McQuaig addressing New Democrat MPs and the caucus room decked out like a political rally for a televised speech by NDP Leader Tom Mulcair
Goodale dismissed Masse's complaint as an attempt by New Democrats to "sling as much mud as they can possibly sling to deflect attention from their own difficulties."
The board of internal economy, which the NDP has derided as a kangaroo court, has ruled that New Democrat MPs improperly used their Commons office budgets to pay for mass partisan mailings and staff in satellite party offices. It has ordered them to repay almost $4 million.
On Wednesday, Liberal MP Marc Garneau asked the board to investigate at least 43 New Democrat MPs who've used their constituency offices to stage door-to-door canvassing blitzes.
New Democrats maintain they're just doing their jobs, meeting with constituents. But the Liberals argue that the canvassing is purely partisan, aimed at identifying potential supportive voters in advance of this fall's election.
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