The US said a 25% tax on steel and 10% tax on aluminum from the EU, Mexico and Canada will start at midnight.
The move immediately triggered vows of retaliation from Mexico, Canada and the EU, which called the tariffs “protectionism, pure and simple”.
The UK said it was “deeply disappointed” by the US decision, which followed weeks of negotiations.
The tariffs will hit products such as plated steel, slabs, coil, rolls of aluminum, and tubes, raw materials which are used extensively across US manufacturing, construction, and the oil industry.
EU trade commissioner Cecilia Malmstrom said it was a “bad day for world trade”, while European Commission president Jean-Claude Juncker said the move was “totally unacceptable”.
The EU has “no choice” but to bring a case before the World Trade Organization and impose duties on US imports, he added.
Canadian Prime Minister Justin Trudeau said the tariffs were an “affront” to the longstanding relationship between Canada and the US, especially to the “thousands of Canadian soldiers who fought and died alongside their American comrades-in-arms” in Afghanistan.
He said Canada plans to levy tariffs on American products worth about $13bn starting 1 July. It is also planning a challenge at the World Trade Organization.
He said: “We have to believe that at some point common sense will prevail but we see no sign of that in this [US] action today.”
What American products will be affected by retaliation?
Media captionTrudeau: Canada not US national security threat
Canada said it would put 25% tariffs on certain types of American steel, as well as a 10% tax on other items, including yoghurt, whiskey and roasted coffee.
Mexico’s Economy Ministry said it is planning new duties for steel, pork legs and shoulders, apples, grapes, blueberries and cheese. Europe had previously outlined a list of items, including US bourbon, cranberries and jeans, as targets for retaliation.