The trade case against Bombardier, which was brought by the American aerospace giant Boeing, is typically a dry and routine affair. It centers on government subsidies and accusations of unfairly low sales prices.

But now trade is politically charged.

Prime Minister Justin Trudeau of Canada has asked the American president to intervene to persuade Boeing to drop the case against Bombardier. Prime Minister Theresa May of Britain joined the chorus of criticism against the United States, since the wings for the aircraft, the CSeries, are made in Northern Ireland. It also soured the mood for the latest round of Nafta negotiations, which finished on Wednesday in Ottawa.

Speaking from the conclusion of the talks, Chrystia Freeland, Canada’s foreign affairs minister and the lead minister on the Nafta talks, said the country would “fight very, very hard” when it came to Bombardier. Ms. Freeland said she had raised the issue with Robert Lighthizer, the United States trade representative.

“I do want to remind Canadians that aggressive actions and aggressive decisions by commerce are nothing new,” she added, a reference to the United States Commerce Department, which imposed the tariff on the Bombardier aircraft. “They are certainly familiar to us from the softwood lumber dispute.”

After an official visit to China, Wilbur Ross, the secretary of commerce, told a group of reporters in Hong Kong on Wednesday that Boeing had initiated the case, not the Trump administration. But he nonetheless emphasized that it was emblematic of the president’s aggressive posture on trade.

Mr. Ross said the administration had been “much more enforcement oriented” than its predecessors. “I wouldn’t be surprised if that trend continues,” he said.