Tom Mulcair's grip on the NDP appears increasingly tenuous, with an open letter calling for "renewal" and one of his high-profile MPs is refusing to publicly support his leadership.

Niki Ashton, holding a news conference in Ottawa about the employment challenges facing young Canadians, was asked repeatedly if she endorsed Mulcair as leader, but refused to give a straight answer.

"This is not about a person or a personality," she said. "Those processes are in place and will take their course. It is about ideas and I'm proud to be putting forward an idea or call to action that is critical."

Ashton ran against Mulcair in the leadership contest on March 24, 2012.

Her news conference comes as 37 Quebec-based activists, riding association presidents, organizers and former MPs issued an open letter in Le Devoir newspaper calling for "renewal" in the party.

Division in the NDP over future leadership11:20

The NDP has been carrying out a post-mortem in the aftermath of last fall's devastating finish in the election campaign, when they dropped to 44 seats in the House of Commons from the previous 95.

Only 16 MPs are from Quebec.

Possible leadership review

Mulcair later wrote a personal letter to supporters taking full responsibility for those results after a preliminary working group's report found the party's message failed to resonate 

A policy convention and vote on a possible leadership review will be held in Edmonton next month. More than 50 per cent voting "yes" would automatically trigger a leadership review, but NDP president Rebecca Blaikie has suggested 70 per cent should be the appropriate bar for approval.

Former Quebec NDP MP Jamie Nicholls, one of the signatories of the open letter, agreed the party should look for a new leader if Mulcair can't meet that 70 per cent threshold. Speaking on CBC News Network's Power & Politics, he did not directly blame Mulcair but said the NDP has failed to engage and inspire Canadians.

"The thing to be doing right now is listening and respecting the voices of the membership," he told host Rosemary Barton. "It's larger than Tom Mulcair — it's the future of our movement."

Holding a news conference in Toronto today, a group that calls itself the NDP "socialist" caucus ramped up its campaign to replace Mulcair. 

NDP Socialist Caucus calls for Leadership review1:24

Chairman Barry Weisleder said the party has strayed too far from its democratic, social justice roots. Mulcair should not be "rewarded" for losing 60 per cent of the party's seats and one million votes in the last election, he said.

"The problem is capitalism, not mismanagement of the deck chairs on the Titanic," he said. "The importance of the leader should not be exaggerated to the detriment of other factors. We are mindful of the fact that big change comes from the bottom up, but in order to open the doors and windows to a more democratic and socialist process, there is no choice now than to vote for leadership review in Edmonton in April."

Changes to avoid mistakes

Mulcair has said he's committed to remaining at the helm and promised to bring in changes to ensure mistakes of the last campaign are never repeated.

A party official noted that Mulcair has also received public words of praise from key union leaders and caucus members in the aftermath of the election. 

Nevertheless, the criticism keeps mounting.

Today, two NDP student groups from Montreal's Concordia and McGill universities issued a blistering statement condemning the electoral platform and urging the party to return to its role as the social conscience of the nation.

It came under the heading "Mulcair Must Go."

"While Mr. Mulcair is a respected politician, we do not feel he shares our values as social democrats," it reads. "His long career in the Quebec Liberal Party leaves him disconnected from the social movements, unions, and student movements that have traditionally been the lifeblood of the NDP. "