Prime Minister Justin Trudeau is about to become the target of sharp criticism at home over his government's handling of NAFTA negotiations.

The Conservatives say they are "frustrated" with the way the Liberals have managed the talks to date and will be more vocal in highlighting their concerns going forward.

"You're going to hear the Conservatives be louder," said Erin O'Toole, the Conservative foreign affairs critic.

"It is a crisis. Canada's backed into a corner. So we are worried the Trudeau plan has not worked."

Foreign Affairs Minister Chrystia Freeland is expected to return to Washington this week for another round of high level talks with her American counterparts.

The U.S. and Mexico already have reached an agreement in principle and are threatening to move on without Canada if Ottawa isn't ready to sign by October 1.

CBC News has reported previously that Canada is prepared to play the role of deadline spoiler, as Canadian negotiators work toward a deal they are comfortable signing.

While no Canadian officials have said talks are in crisis mode, sources say progress is "slow."

O'Toole has been careful to make the point that he still hopes Canada can get a good deal, and that when speaking about NAFTA in the United States or abroad, the Conservatives will still be a part of the 'team Canada' approach.

"We don't go to Washington to have our political discussions for Canada," O'Toole said.

Conservative MP Erin O'Toole says his party is going to be 'louder' in its criticism of the way the Liberals have handled NAFTA negotiations. (Sean Kilpatrick/Canadian Press)

He added the Conservatives are willing to help when called upon, even though they disagree with the approach the government has taken so far.

O'Toole said Ottawa should not have tried to add new "progressive" elements to NAFTA.

When Canada announced its negotiation goals last year, it included a push for provisions on gender, Indigenous rights, and the environment.

"The so-called Trudeau agenda was inserted, and went over very poorly in the United States," said O'Toole. "So we squandered the early six months of negotiations and I think we're paying for it now."

NAFTA talks, for the most part, have not been subject to partisan political attacks in Canada.

"I think it's been very difficult under the Donald Trump administration to negotiate. We recognize that," said NDP trade critic Tracey Ramsey.

She said the NDP will be questioning the Liberals about NAFTA in the fall session of Parliament and that it will "factor hugely" into the 2019 federal election campaign.

NDP MP Tracey Ramsey says NAFTA negotiations will be a factor in the 2019 federal election campaign. (CBC)

"There are points where we are going to push on the government to do better," Ramsey said during an interview with CBC News.

"We are vehemently opposed to opening up supply management any further than it has been already ... it seems to be a favourite kind of concession of the Liberal government and the Conservatives before us. We want that to end."

Sources have told CBC News that Canada is willing to make concessions on dairy supply management which would allow American farmers to sell more products north of the border.

A senior source with direct knowledge of the situation said negotiators are still working out what new regulations would look like.

Foreign Affairs Minister Chrystia Freeland looks on as United States Trade Representative Robert Lighthizer delivers a statement to the media on Jan. 29. Trudeau has to have a narrative that says 'I stood up to the Americans,' say political observers. (Graham Hughes/Canadian Press)

Concessions wouldn't necessarily be a domestic political death blow for the Liberals, said Shachi Kurl, executive director of the non-profit polling foundation Angus Reid Institute.

"If we get to an agreement, it's not as though Canadians are going to be reading it line by line clause by clause and making decisions based on the substance of the deal, as much as they will be listening to the narrative," Kurl said during an interview with CBC News in Montreal.

"For Justin Trudeau, that narrative has to be, 'I stood up to Donald Trump, I stood up to the Americans and I got the best deal that I could.'

"For Andrew Scheer, that narrative is Justin Trudeau failed. He went to the fair, he sold the cow for a handful of beans and it was a really really bad deal."