Opponents of Canada's $15-billion arms deal with Saudi Arabia are taking Ottawa to court in an attempt to block shipments of the combat vehicles, a move that could force the governing Liberals to explain how they justify the sale to a human-rights pariah under weapon-export restrictions.

Daniel Turp, a professor of international and constitutional law at the University of Montreal, is leading the effort, supported by students and a Montreal law firm with a record of class-action work and anti-tobacco litigation.

He will announce the legal challenge on Saturday and intends to file it with the Federal Court within three weeks.

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Mr. Turp and his group are calling on critics of the deal across the country to rally behind their challenge, which they are calling Operation Armoured Rights, pointing to how poorly Saudi Arabia treats its own citizens and the civilian carnage of the Saudi-led bombing campaign in Yemen.

There is evidence Prime Minister Justin Trudeau is out of step with the majority of Canadians by refusing to cancel the deal. The manufacturer, General Dynamics Land Systems in London, Ont., is still gathering material for production.

A poll by Nanos Research suggests most Canadians consider the massive arms sale out of line with Canada's values and believe human rights should trump jobs. The survey showed nearly six in 10 feel it is more important to ensure arms go only to countries "that respect human rights" than it is to support 3,000 jobs by selling weaponized armoured vehicles to Saudi Arabia.

A spokesman for Foreign Affairs Minister Stéphane Dion declined to comment on the poll on Friday.

The Canadian government is the prime contractor in the deal to sell combat vehicles with machine guns and anti-tank cannons to the Saudi force that protects the Mideast kingdom's monarchy from internal threats. The deal is expected to include upward of 1,000 fighting vehicles, plus service and training.

The watchdog organization Freedom House regularly ranks Saudi Arabia among the "worst of the worst" on human rights.

The Federal Court challenge will argue that the Canadian government is violating its own arms-export rules by permitting the armoured vehicles to be shipped to Saudi Arabia. It will ask the court to rescind any export permits that have been granted for the fighting vehicles and block any future ones.

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Canada's export controls place restrictions on sales to countries with a "persistent record of serious violations of the human rights of their citizens."

The federal government is supposed to assure itself the Saudis will not turn the light-armoured vehicles (LAVs) on civilians. The rules say shipments cannot proceed "unless it can be demonstrated there is no reasonable risk that the goods might be used against the civilian population."

Mr. Turp, a former Bloc Québécois MP who later was a Parti Québécois MNA, said he finds it hard to believe Mr. Dion, once a professor at the University of Montreal himself, really believes the Saudi deal is appropriate.

The Trudeau government has rebuffed repeated requests to spell out how it justifies export of these arms, saying this might hurt the "commercial confidentiality" of the deal.

"The idea that military equipment made in Canada could contribute to human-rights violations against civilians in Saudi Arabia and neighbouring countries is immoral. But we also believe that the authorization to export armoured vehicles to Saudi Arabia is illegal," Mr. Turp and the legal campaign's supporters write in an open letter.