NDP Leader Tom Mulcair is trying to stake out new ground to the left of the Liberals ahead of his much anticipated leadership review at the party's upcoming convention in Edmonton.

The Montreal-area MP has faced criticism from some of the party's base for his shift to the centre in the last election campaign. But now, in the wake of the Liberal government's first budget, he's painting his party as a progressive bulwark.

"People know who the NDP are and they also know that the last time the Liberals were there they wound up imposing really strict austerity measures under [former prime minister] Paul Martin," Mulcair said in an interview with CBC Radio's The House.

Mulcair said Finance Minister Bill Morneau's budget was costly and yet failed to address some key election promises, including money for indigenous youth, home care and a tax on stock options.

He also said employment insurance reforms still leave too many families unable to access the program.

"Here we have the Liberals spending a lot — a $30 billion deficit — it's not a question of deficit or no deficit it's a question of, 'OK what are we getting for it?'"

But the leader said he understands why some NDP voters have voiced support for the budget. "Don't forget the starting point is Stephen Harper's 10 years of Conservative rule …This is a heck of a lot better than what we were getting."

While Mulcair might be demanding more spending than what the Liberals promised in Wednesday's budget, that position is a major shift in how he campaigned in the last election.

He presented the NDP as a party with a history of fiscal prudence and he pledged to balance the budget if elected.

Possible leadership review

NDP members will now vote April 10 on whether to launch a leadership review, and that balanced-budget pledge still hangs over his head.

Party president, Rebecca Blaikie, who led a cross-country review of the election results, has said the promise to balance the books hurt the party with its progressive base.

"Our balanced-budget pledge was, in part, responsible for presenting us as cautious change," Blaikie said in a note to members.

Some have suggested that Mulcair will need roughly 70 per cent support to stay on as leader, but Mulcair himself has not provided a figure.

Mulcair faces a tough fight at the party's upcoming convention in Edmonton as some key constituencies are voicing opposition. (Fred Chartrand/Canadian Press)

"I've gone across the country and I've met with thousands of members and, importantly, I've met with hundreds of people who will be delegates in Edmonton," he said. "No other leader goes through this every two years but I wouldn't change it for the world."

'Mulcair must go'

A successful result in April might be difficult for Mulcair considering the backlash he is facing from some in Quebec, where a group of 37 New Democrat activists, including three defeated MPs, recently went public demanding a new direction for the party. Party chapters at McGill and Concordia universities have also condemned the leader, saying "Mulcair must go."

He has the backing of the Quebec MPs in his caucus, who recently signed a letter expressing support for his leadership. But the opposition emanating from Quebec could be problematic for Mulcair, who was elected in part as a leader who could maintain the party's strength in that province.

He is also facing criticism from some members of the country's labour movement, a crucial constituency. Sid Ryan, a former president of the Ontario Federation of Labour, recently came out swinging against the leader.

Thirty members of Niagara Regional Labour Council — an area of Ontario where the party performed well in the last election — passed a motion to not support Mulcair in Edmonton, saying "we've got the most right-wing leadership the NDP has had."

Not to mention two of the party's most prominent MPs, Nikki Ashton and Charlie Angus, have not outright endorsed the leader when asked directly.

Mulcair batted away those concerns, saying he has also had support from other circles.

"I think that, overall, if you look at the number of very strong statements of support that I've had in caucus and major players in the labour movement and other groups, I'm not taking anything for granted, but I'm heartened by the level of support."

Several high-profile caucus members have expressed support for Mulcair, including Quebec MPs Alexandre Boulerice and Ruth Ellen Brosseau and B.C. MPs Nathan Cullen and Peter Julian, as well as the national director of the United Steelworkers union.