The US said the tariffs on imports from the EU, Mexico and Canada will start at midnight.
European Union trade commissioner Cecilia Malmstrom said: "Now (Frankfurt: 11N.F - news) that we have clarity, the EU's response will be proportionate and in accordance with WTO rules". "This is protectionism, pure and simple", Juncker said.
"One can think about making voters happy by saying, 'I have a victory, I'll change the rules, you'll see.'" But Macron said those "who waged bilateral trade wars. saw an increase in prices and an increase in unemployment".
"It's entirely up to U.S authorities whether they want to enter into a trade conflict with their biggest partner, Europe", Le Maire told reporters after the meeting.
But he had granted an exemption to the EU, Canada and Mexico.
"Throughout these talks, the USA has sought to use the threat of trade restrictions as leverage to obtain concessions from the EU".
Malmström added the EU's response will be "proportionate and in accordance with WTO rules", and the "US measures clearly go against agreed global rules".
"The UK and other European Union countries are close allies of the United States and should be permanently and fully exempted from the American measures on steel and aluminium".
Back in March, Malmstrom said her tit-for-tat list included iconic USA products such as Levi jeans, bourbon, peanut butter, cranberries and orange juice.
On Thursday, EU Commission president Jean-Claude Juncker said the 28 EU member countries would challenge the tariffs and "impose their own balancing import duties on USA goods like Florida orange juice, and bourbon whiskey".
Now, both of those men have left the White House, and Trump has gravitated instead toward seeking the counsel of trade hard-liners such as Commerce Secretary Wilbur Ross, senior adviser Peter Navarro, and U.S. Trade Representative Robert E. Lighthizer.
"That Canada could be considered a national security threat to the United States is inconceivable", MrTrudeau said.
The EU is expected to respond with tariffs on a little more than $3 billion worth of American goods including motorcycles, bourbon, and blue jeans.
The decision seems purely political, insofar as the Trump administration failed to secure any meaningful concessions from China during the recent trade spat, and so a "win" elsewhere was likely sought after.
European officials had braced for the tariffs and the EU has threatened to retaliate against USA orange juice, peanut butter and other goods in return.
Finance Minister Bill Morneau announced late Wednesday that Canada has expanded the scope of its country of origin marking regime for steel and aluminum products to better determine where they come from.
The move is likely to trigger serious retaliation from the three countries and push the United States to the edge of a trade war. One of the five major themes of the summit will be how countries can find economic growth. "It's totally unacceptable that a country is imposing unilateral measures when it comes to world trade".