Buffett has previously expressed concerns about tariffs, opposing Trump's trade proposals during the 2016 campaign, when he called them "a very bad idea"

Donald Trump on Monday said that Canada and Mexico can't avert his sweeping tariffs, due to come into effect on Tuesday.

Warren Buffett says tariffs are “an act of war, to some degree.” Berkshire Hathaway’s chairman and chief executive said the country has had a lot of experience with tariffs, and that over time they are a tax on goods.