The ministers requested that Treasury Secretary Steven Mnuchin "communicate their unanimous concern and disappointment".
A Commerce Department investigation earlier this year determined a need to ensure adequate USA steel production capacity to supply the military.
"This doesn't happen that often at G7 meetings, but it was the USA against everyone else", Aso told reporters.
"This is $16.6 billion of retaliation", Foreign Affairs Minister Chrystia Freeland said Thursday. "It is undecided at this moment, but we are considering it", Aso told reporters when asked about the possibility of a WTO action against the USA levies.
Brussels has lodged an eight-page list at the World Trade Organization of goods it would hit with retaliatory measures.
On Thursday, Prime Minister Justin Trudeau said the steel and aluminum tariffs were "totally unacceptable".
Finance Minister Bill Morneau said at the start of the three-day meeting on Thursday that the "absurd" tariffs will "absolutely" be the focus. "We are expecting everybody to play by the rules".
"I think the Canadian government did as much as they could to avert this outcome, they've tried engagement and continue to do so".
The statement singled out the Americans, the largest and most important member of the G-7, saying "decisive action" is needed at a leaders summit next week in Quebec.
Canada, Mexico and the European Union were exempted from import duties of 25 per cent on steel and 10 per cent on aluminum when the tariffs were first imposed in March, but those exemptions were set to expire Friday. "The United States must, at long last, be treated fairly on Trade", Trump tweeted. "Highly restrictive on Trade!" The U.S. goods and services trade surplus with Canada was US$8.4 billion in 2017, according to the website.
Larry Kudlow, director of the National Economic Council, tells reporters Friday that he remains optimistic about the outcome of negotiations with Canada, Europe and Mexico in spite of recent escalations.
Days later, however, Peter Navarro, White House trade policy adviser, contradicted Mnuchin in an interview with NPR's Morning Edition.
The US import taxes, which will cost EU firms billions, are coming into force on Friday despite European leaders trying for months to persuade the Trump administration to grant the union a permanent exemption.
Boeing dropped 1.7 percent to $352.16 and Caterpillar fell 2.3 percent to $151.91 while farm equipment maker Deere fell 3.6 percent to $149.51. The broader stock market rebounded on strong monthly jobs data.
"These tariffs are an affront to the long-standing security partnership between Canada and the United States, and in particular, to the thousands of Canadians who have fought and died alongside American comrades-in-arms", he said.
Mexico announced what it described as "equivalent" measures on a wide range of US farm and industrial products, including pork legs, apples, grapes, cheese, steel and other goods. European Union exports subject to US duties are worth 6.4 billion euros ($7.5 billion).
"President Trump has been very clear in wanting to address trade issues", Mnuchin said. The U.S. team also wants to secure greater intellectual property protections and an end to Chinese subsidies that have contributed to overproduction of steel and aluminum.
"The Unite States has been taken advantage of for many decades on trade".
Malmstrom said China's over-production was to blame for the glut of steel that prompted the USA action against its allies. The talks conclude on Saturday.
German MEP Bernd Lange, who chairs the European Union's worldwide trade committee, has said the tariffs are "illegal" and insisted the EU would "make some countermeasures, no doubt about".
Morneau says he expects the G-7 to keep pressure on the US with the hope the Trump administration reconsiders. Opponents of the tariffs on European and North American metals say the administration is hurting allies when it needs them most to put pressure on Beijing.