On Wall Street, the Dow Jones Industrial Average is down 145 points or 0.62 per cent.
"This is protectionism, pure and simple", European Commission President Jean-Claude Juncker said in a statement.
Sky News US correspondent Mark Austin said: "It's not a good atmosphere for any sort of negotiations about a separate trade deal between Britain and the US in a post-Brexit world".
"And, in the case of the United Kingdom, where we send steel to the United States that is vital for their businesses and their defence industry, it is patently absurd".
"The EU does not pose a national security threat to the USA and therefore should not be the target of such measures".
"The UK and other European Union countries are close allies of the U.S. and should be permanently and fully exempted from the American measures on steel and aluminium". He said he planned to travel to China on Friday for trade talks between the world's two biggest economies.
The tariffs add to mounting worries over a trade war as the Trump administration also considers tariffs on USA auto imports - which could hit top suppliers from Mexico, Canada, Japan and Germany - and plans to levy duties on $50 billion in Chinese goods. But the NAFTA talks stalled.
The European Commission's top trade official, Cecilia Malmstrom, said they had repeatedly pleaded with U.S. Commerce Secretary Wilbur Ross to forgo the tariffs and try to come up with a joint solution.
Abramovich's Israeli move allows him to enter Jersey
Abramovich has seen a very lengthy delay over the renewal processing of his UK VISA , which expired in April. The UK said this month it would review long-term visas of wealthy Russians after the poisoning.
But the Trump administration hasn't hesitated to reach for any tool in its arsenal to tackle what it sees as unfair trade.
The three allies were previously given temporary exemptions from the duties - 25 percent on steel imports and 10 percent on aluminum.
The euro reversed earlier gains as inflation in the eurozone rose to the ECB's target in May, fueled by a huge increase in oil prices as the USA made a decision to pull out of a nuclear deal with Iran.
But aluminum prices have already risen as buyers have hoarded the material. Every year, Canada produces about 13 billion tonnes of steel and 3.2 million tonnes of aluminum.
"We're shipping steel to California for some work and I imagine that's going to stop completely", said Furlong, who runs Calgary-based steel fabrication company Furlong Steel. But on Wednesday night, Canadian and Mexican officials learned of the impending tariffs from news reports, according to one US industry official who spoke withPolitico.
"Without a strong economy you can't have strong national security", Ross said. "They're critical for national security". But there was an unwritten agreement that WTO member countries would use the national-security justification sparingly to avoid abuses.
Now that Trump has broken the taboo, critics fear that other countries will impose sanctions.
Mr Fox said: "It's very disappointing that the United States has chosen to apply steel and aluminium tariffs. all in the name of national security".
A list of countermeasures would include tariffs on US metals and food products such as yogurt, pizza and cucumbers, as well as household products like mattresses and refrigerators.
"The administration's trade remedies should specifically target structural aluminum overcapacity in China, which is caused by rampant, illegal government subsidies", said Heidi Brock, president of the Aluminum Association, which represents aluminum producers, fabricators, recyclers and suppliers.
Ross said talks with the European Union had failed to reach a satisfactory agreement to convince Washington to continue the exemption from the tariffs imposed in March.
But Macron said those "who waged bilateral trade wars ... saw an increase in prices and an increase in unemployment". "If anything, this kills the possibility of deals".
Trump has claimed that the tariffs relate to issues of national security, but Trudeau scoffed at such reasoning during a press conference, pointing to several instances where Canadian personnel and USA troops fought side by side, most notably in both major world wars and Afghanistan.