President Donald Trump on Friday threatened to impose tariffs on Canada in retaliation for wildfire smoke, but it was not clear that he has the legal authority to impose such a levy.

“We are holding Canada responsible for the fact that they are not properly maintaining their Forests, and Brush therein, and the United States is being unnecessarily invaded by filthy, polluted, and unhealthy air, the quality of which is dangerous, and totally unacceptable!” he wrote on Truth Social.