From the article:

The move comes one day after Trump threatened to impose tariffs in retaliation for wildfires in Ontario that sent thick smoke pouring into the United States late last week. After watching Sunday’s World Cup final alongside Canadian Prime Minister Mark Carney, Trump told reporters that the subject had come up.

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On Monday, however, a senior administration official said the president’s latest tariff action was unrelated to his irritation over the wildfires. Instead, the official said, the president was acting in response to Canada’s retaliation for emergency tariffs Trump imposed in April 2025, when U.S. alcohol was removed from Canadian store shelves. The administration has also complained about Canadian limits on auto imports and dairy products.

Monday’s action relies on a never-before-used provision of a 1930 trade law, which provides for tariffs of up to 50 percent against countries that discriminate against U.S. goods. The 30-day delay provides time for the two nations to resolve the dispute before tariffs take effect.

If the tariffs do take effect, they will apply to most Canadian goods, including those that qualify for duty-free treatment under the United States-Mexico-Canada Agreement that Trump negotiated during his first term. Energy, potash fertilizer, critical minerals, fish and products covered by existing national security tariffs will be exempt, said the administration official, who briefed reporters under ground rules that did not allow them to be identified.