Macron made his views clear to Trump by phone on Thursday after the US announced the tariffs on products from the EU, Canada and Mexico to come into effect as of Friday.
Europe is the single-largest source of US steel imports.
Macron warned that the decision would penalise everyone, including the US.
"I think this decision is a mistake in many ways because it responds to existing international imbalances in the worst way -- by breaking up and creating economic nationalism," he said.
"And nationalism is war. That's exactly what happened in the 30s."
EU chief Jean-Claude Juncker says the bloc is poised to announce counter-measures immediately.
France and other European nations will not negotiate while the sanctions were in effect, French Finance Minister Bruno Le Maire said en route to the G7 meetings in Canada on Thursday.
International Monetary Fund chief Christine Lagarde warned the G7 officials of an erosion of trust as the tariff temperature rose.
And she said the action will "distort and damage and disrupt supply chains which have been established now for decades".
Back in the United States, even members of the Republican Party spoke out against the tariffs, US House Speaker Paul Ryan, the most influential Republican in Congress, said he disagreed with the move and said the US should be targeting China instead.
The Trump administration has defended the tariffs as being in the interests of national security, arguing that the country needs to protect its own steel market to produce efficiently in case of an emergency, RFI Washington correspondent Philip Crowther says.
The White House said Thursday the tariffs first imposed in March -- 25 percent duties on steel and 10 percent on aluminum -- have had "major, positive effects on steel and aluminum workers and jobs".
Canada's Prime Minister Justin Trudeau said the US tariffs on his country's products were "totally unacceptable" and vowed to challenge the action in the World Trade Organisation and the North American Free Trade Agreement.
Canada's Foreign Minister Chrystia Freeland announced retaliatory duties on up to 16.6 billion dollars on everything from US steel and aluminum as well as consumer products from 1 July.
The Mexican economy ministry also announced a tit-for-tat move on goods including steel and a wide range of agricultural products.