The Canadian team working on a trade deal with the United States could walk away from talks in the wake of a U.S. decision to impose a 35% tariff on some goods from Canada, an adviser to Prime Minister Mark Carney said on Friday.

Trump has justified tariffs on goods from Canada, the top U.S. export market, by accusing it of failing to stop the cross-border flow of fentanyl, even though U.S. government data shows Canada accounts for only 1% of the fentanyl that enters the United States.

President Donald Trump said the US will put a 35% tariff on some imports from Canada, escalating the tensions between two countries that have impaired one of the world’s largest trading relationships.