French President Emmanuel Macron called the implementation of American tariffs on European steel and aluminum "illegal" and "a mistake" on Thursday during a phone call with President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE.

During the call, which took place late Thursday, Financial Times reports that Macron warned Trump that tariffs on steel and aluminum, which Trump announced Thursday would be implemented after months of negotiations between European and U.S. officials, amounted to "economic nationalism that will penalize everyone including the U.S.," according to an aide.

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."

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U.S. allies cried foul on Thursday after the Trump administration announced the implementation of the tariffs, which are expected to have a major effect on U.S. steel imports from the EU as well as Canada.

European Commission leader Jean-Claude Juncker was one of several officials on Thursday to issue statements condemning the move, which has led to fears of a trade war between the U.S. and countries once thought to be close allies.

“The U.S. now leaves us with no choice,” said Juncker. “Our U.S. friends are turning their back on anything that smells like multilateralism.”

U.S. analysts have also warned against the new tariffs, which the Chamber of Commerce, a top GOP ally, said Thursday would cost American jobs.

“A growing list of tariffs proposed or imposed by our government, as well as the continued uncertainty over the future of Nafta, threatens to undermine the economic progress we have made,” the group's president Tim Donohue wrote.

Commerce Secretary Wilbur Ross Wilbur Louis RossTrump admin asks Supreme Court to fast-track excluding people in U.S. illegally from census Trump 'very happy' to allow TikTok to operate in US if security concerns resolved TikTok, WeChat to be banned Sunday from US app stores MORE said Thursday that Canada, Mexico and the EU would bear the brunt of tariffs after negotiations with U.S. officials on trade issues took too long.

“Those talks are taking longer than we’d hoped. There is no longer a precise date when they may be concluded, so they were added into [the] list of those who will bear tariffs,” he said.