Prime Minister Justin Trudeau says Canada's response to the Trump administration's threatened 25 per cent tariffs on steel and aluminum will be clear and firm, but stopped short of saying whether Ottawa will respond with dollar-for-dollar counter measures.

U.S. President Donald Trump announced Monday he will impose tariffs of 25 per cent on steel and aluminum against multiple countries, including Canada, in his latest salvo of trade threats against other nations.

The trade war between the United States and Canada officially started with a stroke of President Donald Trump’s pen at around 6 p.m. on Monday. This comes just a week into a promised 30-day pause on a blanket 25% tariff on Canadian goods.

Just one week after Canada was temporarily spared from across-the-board tariffs, U.S. President Donald Trump said he will put 25 per cent tariffs on all of the country's steel and aluminum imports, a move that will particularly sting Canada.