The EU, an aide to Macron added, will "react by taking appropriate measures, in a firm manner and proportionately, in conformity with World Trade Organization rules".
She calls the US measures illegal and counterproductive.
Canadian prime minister Justin Trudeau hit back at the justification, saying: "That Canada could be considered a national security threat to the United States is inconceivable".
Tariff: U.S. plans to impose 10 per cent tariff on aluminum from Canada.
White House National Trade Council Director Peter Navarro discusses the significance of President Trump's steel and aluminum tariffs.
The EU's temporary exclusion from punitive USA tariffs on steel and aluminium "did not appear satisfactory to us", French President Emmanuel Macron said after an EU summit on Friday (23 March).
Eric Miller, of the Washington-based Rideau Potomac Strategy Group, said it is possible to move forward with NAFTA on a separate track from the tariff dispute.
The trade actions have also opened the U.S.to criticism that it's burning bridges just as Trump is seeking to rid North Korea of nuclear weapons and help stabilize the Middle East. The administration has argued that foreign production of steel and aluminum has driven down prices and hurt USA producers, creating what the Commerce Department has called a national security threat.More news: Nashville prepares for 3rd visit from President Trump amidst Blackburn fundraiser
More news: Liverpool goalie received death threats after rough Champions League final performance
More news: Trump's trade agenda hits stumbling blocks in "easy" fight
George said Canada will still work in good faith with the USA on renegotiating NAFTA, as it's critically important for all three countries to come out of negotiations with a deal that benefits all parties.
A statement from Mexico's economy ministry says the USA use of a national security justification is improper and that the tariffs affect strategic sectors for North America, including automotive, aerospace and electronics.
Germany's Economy Minister said early this morning that the European Union might look to coordinate its response with Canada and Mexico.
He said he planned to travel to China on Friday for trade talks between the world's two biggest economies.
"This is not the way we do business, and certainly not between longstanding partners, friends and allies", EU Trade Commissioner Cecilia Malmstrom said in a statement. He justified the tariffs by arguing that United States producers are vital to national security and were threatened by a global supply glut. She said if there were no exemptions, "We will respond in an intelligent, decisive and joint way".
"Our steel and aluminum industries are a source of critical supply for American manufacturers and its defence industry".
As a precautionary measure, the commission, notified the World Trade Organisation of eventual counter duties on May 18 that could come into force 30 days later and would affect some 2.8 billion euros in products.
She was the latest European politician to hit back at the USA decision, which has was described by President Emmanuel Macron of France as a "mistake" and the worldwide trade secretary, Liam Fox, as "patently absurd". "The goals of restoring American industries to a sustainable operating domestic capacity and protecting national security must remain paramount".
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 the broader market sank because of trade war fears.
Germany has tended to favor a more conciliatory approach, while others believe, after weeks of metal tariffs talks, that Trump will only respect a hard line.