The tariffs took effect early Saturday after three days of negotiations in Washington between Canadian Trade Minister Dominic LeBlanc and U.S. Trade Representative Jamieson Greer failed to resolve differences. The new U.S. measures cover about 5% of Canadian exports to the United States and are being imposed under Section 338 of the Tariff Act of 1930, a little-used provision that allows tariffs of up to 50% in certain cases. The duties add to existing U.S. tariffs affecting Canadian steel, lumber and automobiles, increasing pressure on trade between countries whose economies and supply chains have long been closely integrated.

Canadian Prime Minister Mark Carney said Ottawa had halted negotiations and would answer the new tariffs on a dollar-for-dollar basis after the United States made changes to proposed terms late in the talks. The new duties also apply to some goods that qualify for preferential treatment under the U.S.-Mexico-Canada Agreement, or USMCA, which has protected much of the bilateral trade relationship from earlier tariff actions. The breakdown comes as the countries face broader questions over the future of their trade relationship and the upcoming review of the USMCA, the agreement that replaced the North American Free Trade Agreement in 2020.