President Donald Trump’s long-threatened tariffs have gone into effect, kicking off a trade war with America’s neighbors.

New 25% trade tariffs on goods from Canada and Mexico went into effect early Tuesday after President Donald Trump declined to extend a 30-day pause in a move the president says aims to quell the flow of illegal drugs like fentanyl into the U.S. The new assessments also include a 10% tariff on Canadian energy products.

Mexico and Canada vow to retaliate against sweeping tariffs imposed Tuesday by President Trump on all goods from their countries, a move that overnight upended free trade in North America.