In a telephone call with Trump, the French leader expressed his “deep concerns”, saying the tariffs due to come into effect in two weeks “risk triggering a trade war, in which all affected countries would be losers”, Macron's office said.
He also argued that “such measures against allied countries, who respect international trade rules, would not be effective in fighting unfair practises” and said the European Union would respond in a “clear and proportionate manner to all practises that are unfair or contrary to international trade rules”.
On Thursday, Trump defied warnings from US allies in announcing tariffs of 25 percent on imported steel and 10 percent on aluminium.
He said they would not initially apply to Canada and Mexico, and that close partners on security and trade could negotiate exemptions.
EU Trade Commissioner Cecilia Malmström has said the bloc is “counting on being excluded”, but Brussels has already drawn up a list of American products to target for countermeasures if its exports are affected.
Macron also called for “tough talks” with Pyongyang as he spoke to Donald Trump and hailed plans for a historic meeting between the US and North Korean leaders.
“The international community must maintain its unity for tough talks with North Korea to pave the way for a denuclearisation of the Korean peninsula,” Macron's office quoted him as telling the US president in a telephone call.
The move is a high-stakes encounter for both Trump and North Korea's Kim Jong Un, who have traded insults in the past and threatened to wipe out each other out.
News of the summit, which South Korean President Moon Jae-in said was “like a miracle”, is the latest step in a quickening detente.
North and South Korea exchanged envoys as Pyongyang sent a delegation to the South's Winter Olympics, which Seoul had dubbed the “Peace Games”.
The thaw came after a period of extreme tension between Washington and Pyongyang.