Thomas Mulcair is making a pitch to centrist voters with his openness toward a free-trade deal with the European Union, but it is a fine line for an NDP Leader who must keep a close eye on his own MPs and the party's left flank.

The NDP's position is that it "welcomes" the deal but is staying neutral until a final text is released in a few months. Yet some NDP MPs are already speaking out.

NDP MP Ryan Cleary said he fears his province of Newfoundland and Labrador is giving away its fishery by surrendering a requirement that minimum amounts of fish that are caught in area waters are processed in the province. "I have to stand up for my province when I see something that could have such a massive impact on rural communities," he said, adding that voices of concern in the province are increasing. "Giving up minimum processing requirements is a big deal, but it's being treated like it's not," he said.

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Mr. Cleary added that he supports his party's position to remain neutral on the draft Canada-European Union Comprehensive Economic and Trade Agreement (CETA) until a final text is released, but his comments suggest he would have a hard time voting in favour of the deal.

Even after the final text is released, trade critic Don Davies said the NDP will hold public consultations on the final wording before taking a position.

Conservatives say the NDP's wait-and-see position makes little sense given that many other groups feel they have enough information to agree or disagree with the deal and polls show most Canadians are in favour.

The NDP's 2011 campaign director Brad Lavigne, who has just released a book about his time inside the NDP working for former leader Jack Layton, said it would clearly help Mr. Mulcair in the next election if the NDP decided to support CETA.

"Heading into that election with an understanding that trade is good will undoubtedly be to the New Democrats' benefit," he said, adding that critics must also feel they've been heard. "Just because there are voices within the progressive side of the ledger doesn't mean that the party has to go along with that group … It will speak to Mr. Mulcair's ability to make a decision, despite a handful of voices who dissent."

There are already signs the debate could prove challenging for some in the caucus – including Quebec MPs. "The main source of feedback is anger, to be frank with you," said Mathieu Ravignat, who has been hearing from dairy farmers in his Quebec riding of Pontiac. That anger from farmers is directed at the government, not the NDP, he said. The MP said his party's wait-and-see approach is the right stand, "for now."

There is also concern among New Democrats that the party could find itself offside with supporters in the labour movement over the deal's provisions that open up municipal and other government procurement contracts to European firms.

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Paul Moist, the Canadian Union of Public Employees president, has many concerns about CETA but said Mr. Mulcair is working hard to explain the NDP's position to unions.

"I don't think it's a fait accompli that the NDP's going to endorse [CETA], but he's smart to keep his powder dry in my opinion," Mr. Moist said.

Council of Canadians president Maude Barlow is concerned the NDP is placing politics above principle.

"We don't need the NDP worrying about optics, for heaven's sake," she said. "We need them standing up for the core values that they've always stood for."