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.

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.

President Donald Trump threatened to unleash tariffs of 35% on imports from Canada starting on August 1 as he continued his attack on the US' neighbor.