Europe had promised swift retaliation if it was hit with the trade penalties, and had warned it could quickly respond with 25% tariffs on U.S. products such as motorcycles, denim, cigarettes, cranberry juice and peanut butter.
Trump had offered the two USA neighbours a permanent exemption from the steel and aluminum tariffs if they agreed to U.S. demands on NAFTA. Like the European Commission president, Trudeau also said that they may challenge the move at the World Trade Organization.
In a joint statement, the six finance ministers, without the support of the United States, called for "decisive action" following the Trump administration's decision to impose tariffs on Canada, the European Union and Mexico this week.
Trump responded to the Canadian tariffs on up to $16.6 billion worth of US imports, saying the days of the USA being taken advantage of in trade deals "are over".
"It's a sad day for worldwide trade", said the economy secretary today, describing the United States' announcement of metal tariffs against its trade partners as "completely incomprehensible".
Quitting NAFTA would be yet another explosive and controversial trade move by the Trump administration. "The European Union can not react to that without any kind of reaction".
With luck, the US president will think again about his whole approach to trade and global relations, recognize the costs, and back off.More news: Rockin' Relay: Cancer Society benefit brings hundreds out
The tariffs are aimed at allowing the USA steel and aluminium industries to increase their capacity utilisation rates above 80 per cent for the first time in years.
Mr. Trump says - as he has many times before - that NAFTA has been a awful deal for the United States, while its North American trading partners make "many billions of dollars" at the expense of Americans.
The minister says she doesn't believe the tariffs will alter the government's plan to purchase new military gear from the US because extra money is typically set aside for unexpected circumstances.
But she says they could hit Canadian businesses, some of which say they are watching closely to see how the dispute unfolds.
Secretary of Commerce Wilbur Ross said that these tariffs were important for national security.
French Finance Minister Bruno Le Maire also said Mnuchin was alone on the tariff issue, with the group becoming a "G6 plus one" as the six expressed "total incomprehension" over the U.S. move.
France's Finance Minister Bruno Le Maire had met with Ross on Thursday in a bid to end the stand-off over steel and aluminum, a move that ultimately failed to sway the United States administration.
Getting rid of the exemptions for Canada and Mexico, meanwhile, could complicate ongoing negotiations on NAFTA.
"It just doesn't make any sense and we're going to continue to explain that to the president and the American administration", he said on CBC, adding that the relationship had always been "positive and mutually beneficial".