TORONTO -- Justin Trudeau took a day off from the campaign trail on Monday, but his Liberals still ended up in a spat with New Democrats over transit funding.

A spokeswoman for Trudeau refused to discuss what he was doing on a day when both Conservative Leader Stephen Harper and his NDP counterpart Tom Mulcair were visible on the hustings.

"We don't share what the leader is doing on down tour days," Kate Purchase said in an email. "He was up over the weekend when other leaders were not."

The Liberal campaign, however, was not exactly quiet, putting out a media release accusing Mulcair of tearing up a promise to spend $1.3 billion on public transit immediately.

The statement from Adam Vaughan, campaigning for re-election in Toronto, said Mulcair had reneged on the pledge after the Liberals had shown the NDP could not balance the budget and keep its promises.

"Mulcair stood in front of Canada's mayors in June promising more than a billion dollars for public transit next year; now it's a billion dollars less," Vaughan said in the statement.

"He said nothing about a phase-in. Mulcair has broken his public transit commitment to Canadians."

The release drew an indignant response from the New Democrats, who accused the Liberals of "making stuff up" for the second straight day.

"Do the Liberals have so little faith in what Justin Trudeau is saying that they have to lie about Tom Mulcair's concrete plan?" Peggy Nash, a Toronto NDP candidate, said in response.

In fact, the New Democrats said, Mulcair's transit pledge has not changed since it was first put to the Canadian Federation of Municipalities in a speech in June.

They noted the party distributed a background paper that accompanied the speech that clearly shows the funding for his "better transit plan" would be phased in over four years.

According to that paper, an NDP government if elected would spend $420 million in 2016, topping out at $1.3 billion annually starting in 2019.

Vaughan, however, based his release on a line in Mulcair's speech in which he said the NDP would invest $1.3 billion a year -- but did not specifically reference the phase-in period.

The Liberal candidate went on to accuse Mulcair of backing off health-care funding commitments.

Mulcair's promises are "meaningless," Vaughan said.

Trudeau planned to return to the hustings Tuesday.