WINNIPEG -- Manitoba's governing New Democrats are gathering this weekend under a cloud as the party tries to bolster public support amid voter anger and the ouster of a former cabinet minister from the NDP caucus.

The party has slipped in the polls since it raised the provincial sales tax last summer after ruling out tax increases during the 2011 election campaign. In the days leading up to the convention, the party has been rocked by a war of words between Premier Greg Selinger and former cabinet minister Christine Melnick.

Melnick was removed from caucus Tuesday after publicly accusing the premier's office of making her a scapegoat for an immigration debate controversy.

NDP secretary Nanci Morrison said that might be the topic of conversation among some delegates, but she said the convention is about policy.

"We're having no problem having people come to our convention, our dinner is sold out," she said. "I think there are challenges for the party certainly ahead, but the party is well-positioned to meet those challenges."

Pundits and pollsters say the party is in trouble.

The NDP fared poorly in two recent byelections in western Manitoba, struggling to get more than 10 per cent of the vote. Although both seats were considered staunchly Conservative, the NDP came third behind the Liberals in Arthur-Virden.

Pollster Curtis Brown with Probe Research said the NDP is bleeding support to both the Opposition Tories and the Liberals. The NDP is even losing support in Winnipeg -- a necessary stronghold if they want to hold on to power, he said.

"They're not in a good place right now," Brown said. "They're down significantly compared to where they were in the last election and especially, and most importantly, they're down (in) Winnipeg."

When the NDP hiked the provincial sales tax to eight per cent from seven per cent, Brown said support for the NDP went "off a cliff." The party is consistently polling in the high 20s while support for the Conservatives hovers at around 48 per cent.

The Liberals, under new leader Rana Bokhari, are polling around 20 per cent, he said. Although some disaffected New Democrats may habitually park their vote with the Liberals between elections only to change their minds at the ballot box, Brown said this is the longest the Liberals have held that level of support.

Paul Thomas, professor emeritus of political science at the University of Manitoba, said the party is having a tough time controlling the agenda and getting its message heard. While he said the NDP has made some good infrastructure announcements, the government has had a hard time justifying the tax increase.

Melnick's ouster from caucus has also been an unnecessary distraction, he said. The party has to rally the flagging spirits of its troops this weekend and figure out how to wrestle control of the agenda once again, Thomas said.

"They are dispirited," he said. "Even people who have been long-time warriors on the NDP cause may be saying 'I'm not as excited about the party at this point and about the leader perhaps, so maybe I won't work as hard."'

Delegates gathered Friday afternoon and were to begin debating about 150 policy resolutions put forward by the grassroots. The resolutions are not binding on the government.

Selinger is expected to address delegates several times and has said he hopes the controversy over Melnick doesn't overshadow the "many other important topics" the party has to discuss.