Unable to win concessions from from its trading partners ahead of the Friday deadline, the United States has introduced tariffs on steel and aluminum imports from Canada, Mexico and the European Union.
In Canada, Prime Minister Justin Trudeau said the tariffs were "totally unacceptable", and Canada announced plans to slap tariffs on $12.8 billion worth of USA products, ranging from steel to yogurt and toilet paper.
"But the situation is worrying, it could escalate and also the recovery, the economic recovery that we have seen lately not only in the European Union but also globally, risks of course to be diminished by this".
"We can not let any country force our companies to surrender this hard-earned knowledge at its border", EU Commissioner for Trade Cecilia Malmstrom said.
His tweet came Friday, the same day steel and aluminum tariffs were scheduled to take effect against Canada, Mexico and the European Union.
"I strongly support imposing stiff penalties on countries like China, Russia, South Korea and Vietnam to prevent them from illegally dumping steel and aluminum into the US and throughout the world".
On the other side of the argument, as A.P. points out, American ally Japan has already been paying the tariffs.
Macron told Trump in a telephone call that the tariffs were "illegal", and Merkel said the measure "risks touching off spirals of escalation that in the end hurt everyone".
"Trudeau uttered some of the harshest words a prime minister has directed at an American administration in decades", said Toronto Star columnist Chantal Hebert, calling this a "watershed moment in the Donald Trump-era Canada/US relationship".
Industry experts have warned that EU retaliation could encourage the Trump administration to strike back with more trade barriers on items like European cars.
However, the Canadian industry has been less damaged than had been anticipated as duties imposed by the USA government have been passed on to US consumers in the form of higher prices.
U.S. President Donald Trump's tariffs are driving a wedge in the G7 - and laying the groundwork for a potential clash among its leaders next week in Quebec's Charlevoix region.
Well, they have a $2 billion surplus on steel with us.
The U.S. decision came despite last-minute talks in Paris this week to try to reach a deal.
The steel and aluminum tariffs could also complicate the administration's efforts to renegotiate NAFTA, a pact that Trump has condemned as a job-killing "disaster".
That summit, which will be hosted by Prime Minister Justin Trudeau, will also mark Trump's first visit to Canada as president.
Trump had offered the two US neighbors a permanent exemption from the steel and aluminum tariffs if they agreed to USA demands on NAFTA.
"The more Trump is irritating allies and asking Chinese to buy stuff, the better off they are, because he's not sitting there and attacking the hard issues", the person said.
Labour's shadow worldwide trade secretary Barry Gardiner earlier warned the UK Government to "strongly respond" to the move. That's on par with the value of Canadian steel and aluminum exports to the United States. "So it's not like the trade is imbalanced against the US favor on this".