U.S. President Donald Trump has threatened to impose immediate reciprocal tariffs on Canada in response to Canada’s retaliatory tariffs.

In a social media post on Tuesday in which he referred to Canadian Prime Minister Justin Trudeau as “Governor Trudeau,” Trump said that when the Canadian leader imposes a retaliatory tariff on the U.S., the United States’ reciprocal tariff will immediately increase by a like amount.

This week the Trump administration imposed 25 percent tariffs on most imports from Canada and Mexico and a new ten percent tariff on imports from China.

Trump’s warning came after Trudeau slammed Trump’s sweeping tariffs on Canada, calling the U.S. president’s move “a very dumb thing to do,” and vowed a “relentless fight” to protect the Canadian economy.

Trudeau announced that he would immediately implement 25 percent tariffs on 30 billion Canadian dollars’ worth of U.S. goods, followed by an additional 125 billion Canadian dollars’ worth in 21 days.