Quebec farmers gathered in downtown Montreal on Wednesday to protest an interprovincial trade deal they say threatens their livelihood.

Hundreds of farmers from across the province were bused into the city early Wednesday morning to take part in the rally, organized by Quebec's union of agricultural producers (UPA).

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Farmers are worried they will lose money under new trade rules ((CBC/Melissa Kent))

They marched up Peel Street to Ste-Catherine Street, turned left on McGill College Street and stopped in front of Premier Jean Charest's office. Police barricaded the streets and diverted traffic to make room for the farmers.

The union says it is worried about talks around the Agreement on Internal Trade, a proposed interprovincial deal that aims to increase the free flow of people, goods and services across Canada.

The deal — moving toward abolishing interprovincial trade barriers — would affect Quebec's autonomy in agricultural matters, said UPA organizers.

Quebec farmers want to decide how they produce food, rather than having a pan-Canadian organization determining rules, the UPA said.

Farmers' organizations haven't seen any details of the Agreement on Internal Trade, and accused the Quebec Liberal government of hiding its intentions.

"This is a government that puts trade before the regions, before our family farms, and before the quality of products," said UPA president Christian Lacasse.

Under the agreement, Quebec's strict production standards, inspection procedures and labeling rules could be challenged, said Marcel Groleau, president of Quebec's Dairy Producers Federation.

For example, he said, a product cannot be labeled as yogurt in Quebec unless it contains milk. Under the new provisions, however, a producer from outside the province could challenge that.

A spokesperson for Agriculture Minister Claude Bechard said the agreement would not affect products whose supply is controlled by the province, including poultry; eggs and dairy products. And Quebec's standards and labeling regulations are already open to challenges.

As well, the spokesperson said standardizing regulations across the country would provide the province with additional protection from potential international challenges, because it shows there is a consensus in Canada on questions of supply management.

Charest is heading to Whitehorse, Yukon, on Thursday along with his provincial and territorial trade counterparts to ratify the pact after settling details of Chapter 9, which deals with agricultural matters.