Mr Macron pledged the riposte would be firm and proportionate, and in line with World Trade Organisation rules.
"We have not seen any analysis that shows these exports pose a problem to national security", David O'Sullivan, the European Union ambassador in Washington was quoted as saying by the daily.
The Trump administration argues the tariffs are limited and created to save America's ailing metals industry, which is needed for defence and national security reasons.
Trump tells reporters of America's neighbors: "these are two very different countries".
Mnuchin's remarks came moments after Canadian, German and French ministers denounced US President Donald Trump's decision to impose punishing steel and aluminum tariffs this week, describing frustration with a perceived attack on longstanding allies. "It is pure protectionism", she said.
South Korea also received a permanent exemption from steel tariffs, having negotiated instead an absolute quota equivalent to 70 per cent of 2015-2017 imports.
"This is the best possible set of arrangements and really sets the standard in where free trade should be", Treasurer Scott Morrison said in Sydney on Friday.
While the tariffs being higher than expected could certainly have ramifications for United States businesses, experts say they would be permitted under global law.More news: Top North Korean Official Visits President Trump At White House
Officials at the G7 meeting said the tariffs made it more hard for the group to work together to confront China's trade practices, especially when Beijing, like most G7 members, supports the current World Trade Organization-based trade rules and the United States is seeking to go around them.
Canada argued that the retaliatory tariffs on USA goods were legal under World Trade Organization rules since they were equivalent to what they viewed as an improper United States action.
The EU trade commissioner, Cecilia Malmstrom, has said Mr Trump's tariffs are "further weakening transatlantic relations".
German MEP Bernd Lange, who chairs the European Union's global trade committee, has said the tariffs are "illegal" and insisted the EU would "make some countermeasures, no doubt about".
In his second tweet, he wrote, "If we charge a country ZERO to sell their goods, and they charge us 25, 50 or even 100 percent to sell ours, it is UNFAIR and can no longer be tolerated". He told NPR's Audie Cornish: "We are close allies, we the Europeans, to the United States and we can not understand that decision".
The U.S. Commerce Department recently launched an investigation into imported cars, trucks and auto parts. In fact, U.S. Commerce Department numbers show, the United States recorded a trade surplus with Canada for each of the past three years.
The European Commission, which coordinates trade policy for the 28 EU members, has said the bloc should be permanently exempted from the tariffs since it was not the cause of overcapacity in steel and aluminum.
The EU is set to retaliate with tariffs on a range of USA goods from Harley-Davidson motorcycles to blue jeans and bourbon whiskey.