Prime Minister Justin Trudeau is encouraging Canadian companies that work with Boeing to speak out against the U.S. aerospace giant's trade dispute with Montreal-based rival Bombardier.

The comments come after several Canadian companies wrote to the Liberal government urging it to move ahead with its interim plan to buy 18 of Boeing's Super Hornets.

The signatories said the country's aerospace industry stands to greatly benefit from the purchase, an "interim" plan aimed at meeting the military's immediate needs, and asked him to personally ensure the plan moves ahead.

Instead of talking to the government, says Trudeau, those companies should be directing their concerns about the trade battle — and its potential impacts on their business — at the source of the problem.

"They should communicate that message to Boeing," Trudeau said during a wide-ranging news conference in which he also addressed the deficit and proposed tax changes before flying to the UN in New York.

"I encourage people who work with Boeing across the country to tell that company to what extent their actions against Canada's aerospace industry is not in their interest, certainly not in the interests of Canadians."

Report next week

The Liberal government has threatened for months to scrap its interim Super Hornet purchase — a temporary shore-up for Canada's aging CF-18 fleet — at an estimated cost of $6 billion, unless Boeing backs off Bombardier.

But Boeing has shown no signs of backing down.

The company has accused Bombardier of selling its CSeries passenger jets to a U.S. airline at an unfairly low price with help from government subsidies.

The U.S. International Trade Commission will release the preliminary results of its investigation next week and a finding against Bombardier could result in fines or tariffs.

It could also threaten Bombardier's deal with Delta, which involves up to 125 of the Canadian company's CS100 passenger jets.

PM reaching out for political help

The prime minister has gone out of his way to step up pressure on Boeing in recent weeks in the wake of unsuccessful secret talks between the Chicago-based company and the federal government.

That includes calling the governor of Missouri, where the Super Hornets are built, and enlisting the help of British Prime Minister Theresa May, whose country is home to a large Bombardier plant.

Trudeau has also hinted that Boeing could be blocked from taking part in an upcoming competition to replace Canada's CF-18 fleet in its entirety, which will involve buying 88 new aircraft at an estimated cost of up to $19 billion.

Such a course of action is unlikely, given the potential legal implications for the government if it tries to ban a specific company from vying for the contract.

Many defence experts believe the real reason the Liberals wanted to buy interim Super Hornets in the first place was to sidestep the legal quandary associated with their promise not to purchase the oft-maligned F-35 stealth fighter.

The prime minister said Tuesday that he was still hopeful the government, Bombardier and Boeing would be able to resolve the dispute through talks, even after the trade commission's ruling on Sept. 25.

"Regardless of the results of the preliminary ruling," he said, "discussions will continue and we will continue to defend aerospace jobs in this country and the economic growth that comes with it."

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