This Labour Day, union groups are marking what they see as a milestone in their movement — new clout in the NAFTA talks that have unfolded over the last year.

While much has been said about the declining power of unions, labour groups say they're playing a crucial, unprecedented role in the negotiations.

The Liberal government has brought in union leaders, as well as various industry sector stakeholders, to hear broad perspectives on how best to improve the 25-year-old trade pact.

"I can't think of any trade agreement, ever, where labour has played any sort of an active role," said Jerry Dias, national president of Unifor, Canada's largest private sector union which represents the autoworkers. "NAFTA has been a game-changer for the labour movement and how working class people are treated as it relates to trade."

After talks broke off in Washington Friday, Prime Minister Justin Trudeau worked the phones Saturday. Along with calls to former prime minister Brian Mulroney, Trudeau reached out to two of Canada's most powerful union leaders -- Dias and Hassan Yussuff, president of the Canadian Labour Congress.

Trudeau thanked them for their input and offered a status report on talks.

"They're not going to fold. They're not going to carve a bad deal just to appease the Trump administration," Dias said of the conversation.

Dias said the key sticking points — cultural identity, a dispute mechanism and supply management — are significant and he doesn't expect a quick resolution.

Political clout

After unions played a role in ousting the Harper government in 2015, Dias said the Liberal government appears to understand the influence of the labour movement in politics.

"I think they understand that labour is not just a nuisance; that we actually have a voice, we represent millions of people and we're going to play a big role in the politics of the country," he said. "They have a choice. They can exclude us and then we will exclude them, or they can include us."

Unifor national president Jerry Dias says current NAFTA negotations have been a 'game-changer' for the labour movement in Canada. (CBC News)

Adam Austen, spokesperson for Foreign Affairs Minister Chrystia Freeland, said the government values the input of labour groups "immensely" and has consulted them throughout the negotiations.

"Labour unions have played a critical role throughout this negotiation and were crucial in helping shape the Canadian negotiating position, in particular on rules of origin for the auto sector and the deal's labour provisions, both of which have been strengthened, in part due to Canadian ideas," Austen wrote in an email.

Role in shaping Canada's positions

While not directly at the table, union leaders have routinely met with the NAFTA negotiators, have been briefed on developments, and have made trips to Washington during the sessions.

Yussuff, who is on the minister's NAFTA Council, said time will tell how influential their input has been on the final NAFTA deal. But he said for the first time, unions have had a real role in shaping Canada's bargaining positions.

"It's been unique in the sense that we've been able to have some access to learn what's been going on at a relatively early period and more importantly, to remind the government to take care and protect the key sectors that are all driving this economy ... that are going to protect our members' jobs in the long-term."

Trade lawyer Mark Warner said, while the government kept the union leaders abreast of developments through briefings, he's not convinced they had tangible impact on the talks.

"In a concrete sense, has that affected the negotiating positions of the government? I'm not that sure I've seen evidence of that to be honest," he said.

'Progressive' trade agenda

To create distance from the previous Conservatives, the Trudeau government has promised a "progressive" trade agenda to try to incorporate gender equality, environmental protection, Indigenous rights and labour standards into trade agreements.

It's not known what progressive issues will be in, or out of, an updated NAFTA, but new Trade Diversification Minister Jim Carr's mandate letter does not mention advancing a progressive trade agenda.

NAFTA talks will resume in Washington Wednesday, after Donald Trump again threatened over Twitter to shut Canada out of the deal and warned Congress to butt out of negotiations with Canada.

Trump tweeted that "there is no political necessity to keep Canada in the new NAFTA deal."

Andrew Leslie, the parliamentary secretary to the foreign affairs minister, shrugged that off as rhetoric as talks go down to the wire.

"These negotiations have been taking place over the past year," he said in an interview with CBC News Network. "Literally multiple hundreds of issues have been resolved. It's the last three to four and we always expected things to have a certain amount of drama and excitement the closer we got to the finish line."