President Donald Trump late Thursday threatened a 35% tariff on goods imported from Canada, a dramatic escalation in an on-again, off-again trade war with America’s northern neighbor and one of its most important trading partners.

President Donald Trump says he will raise taxes on imported goods from Canada to 35%, deepening a rift between two North American countries that have suffered a debilitating blow to their decades-old alliance.

Trump previously applied 25% tariffs to non-USMCA goods and the new rate, announced in a letter to Canadian Prime Minister Mark Carney and posted on social media, would mean that number rises to 35%, the official said. The U.S. and Canada had been involved in talks to lower tariffs ahead of a self-imposed July 21 deadline.