The leaders of Quebec's four largest political parties, eager to show they will defend the province's interests, called on the federal government Friday to protect the province's dairy industry as NAFTA negotiations continue next week in Washington, D.C.

"I will not accept any agreement that will not be accepted by our dairy producers and entrepreneurs," Liberal Leader Philippe Couillard.

Couillard was at a joint news conference alongside Parti Québécois Leader Jean-François Lisée and Québec Solidaire co-spokesperson Manon Massé at the Longueuil offices of the Quebec farmers' union, known by its French acronym, UPA.

François Legault, the leader of the Coalition Avenir Québec, couldn't make it because he is campaigning in the Saguenay region, but said he supports the farmers as well.

Legault instead had a conference call early Friday with UPA's president, Marcel Groleau.

PQ leader ⁦<a href="https://twitter.com/JFLisee?ref_src=twsrc%5Etfw">@JFLisee</a>⁩ disappointed CAQ leader ⁦<a href="https://twitter.com/francoislegault?ref_src=twsrc%5Etfw">@francoislegault</a>⁩ is not at the meeting this morning. Says he should have made a better effort to be here to show a strong, united front. <a href="https://twitter.com/hashtag/NAFTA?src=hash&ref_src=twsrc%5Etfw">#NAFTA</a> <a href="https://twitter.com/hashtag/Qc2018?src=hash&ref_src=twsrc%5Etfw">#Qc2018</a> <a href="https://t.co/ofezSslsWN">pic.twitter.com/ofezSslsWN</a> —@TurnbullJay

U.S. President Donald Trump has made it plain that American farmers must be able to export more to Canada.

Trump had set a Friday deadline for the talks, but the talks broke off in the afternoon. United States Trade Representative Robert Lighthizer said Washington will resume negotiations with Canada's team on Wednesday.

The U.S. needs to export milk to deal with its chronic oversupply problem — one that Canada avoids with its strict production quotas. The dairy sector was said to be one of the last unresolved items as NAFTA talks continued into Thursday night.

Prime Minister Justin Trudeau has said his government will protect supply management. But Quebec's political leaders say they want to make sure Canadian negotiators don't concede anything. Couillard said the dairy industry in Quebec is "as important for Quebec as the auto industry is for Ontario."

Dairy contributes about $6 billion to Quebec's annual GDP and creates about 80,000 direct and indirect jobs.​

'A strong lobby'

Pascal Theriault, an agricultural economist with McGill University, said an influx of U.S. milk would mean farmers and processing companies in the province would unquestionably take a hit.

In addition, he said the UPA is "still a very strong lobby and they do have somewhat of a vote swing to help in some key ridings."

“The interests of Americans should not be held above our own.” This illustration handed out to media pretty well sums up how Quebec’s agricultural sector feels about any threat to supply management. <a href="https://t.co/FHgTu27om5">pic.twitter.com/FHgTu27om5</a> —@jbernstien

The party leaders, he said, are really trying to send a signal that, "as premier you will defend Quebec's interests as captain Quebec."

Lisée, for his part, said the fact that concessions on supply management are even being considered is proof that Quebec is being "abandoned" in favour of the interests elsewhere in the country.

"If this country works, the interests of Quebec, the west and Ontario will be equally represented and that's not what I see today," he said.

Not everyone in Quebec's dairy industry is in favour of supply management. The CEO of Montreal-based Saputo Inc., one of Canada's largest dairy companies, said earlier this year he wants to put an end to the system.