President Donald Trump’s extra 10% duty on Canada added fuel to the debate over his legal authority on trade, just as the Supreme Court is about to consider a challenge to his global tariffs.

In a Truth Social post on Saturday, he blasted the Ontario provincial government for not immediately taking down a TV ad that features remarks from former President Ronald Reagan criticizing tariffs.

“Because of their serious misrepresentation of the facts, and hostile act, I am increasing the Tariff on Canada by 10% over and above what they are paying now,” Trump wrote.

He didn’t cite a specific law for the extra levy, and the White House didn’t immediately respond to a request for comment.

But because he is adding it to his existing Canada tariffs, the 10% presumably invokes the International

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