May says Britain and the European Union "will continue to work together to protect and safeguard our workers and industries".
"This is protectionism, pure and simple", said Jean-Claude Juncker, president of the European Commission.
The US has also gone to the WTO and launched a case over what it says is intellectual property theft, but the European Union said that although its case is similar, it identifies further potential violations of WTO rules.
A White House official told The Hill that the Trump administration "wanted clarity on" several issues, including a sunset clause, before USA officials met with Trudeau.
Canadian Prime Minister Justin Trudeau said today he offered to go to Washington this week to complete talks on renegotiating the North American Free Trade agreement but that Vice President Mike Pence called and told him a meeting with the USA president would only happen if Trudeau agreed to put a five-year sunset clause into the deal.
University of Ottawa professor Patrick Leblond said in an interview with AFP that Trudeau's newfound swagger "will help the Liberals in the next election".
The group's highly unusual public rebuke of one of its own members called out the USA for hefty steel and aluminum tariffs the Trump administration imposed in recent days on its G7 friends.
European Union trade chief Cecilia Malmstrom says the bloc is taking China to the World Trade Organization over a dispute on intellectual property.
"This is stupid. It's counterproductive", former British minister of state for trade Francis Maude told the BBC.
Plus, tariffs on metal imports from the EU, Canada and Mexico will be put into effect from Jun 1, as exemption offered earlier in the year lapsed.
"The inevitable result of putting these tariffs on imports will be to increase prices on consumer goods for its own citizens".
Morneau has called the tariffs "absurd", saying Canadian metal sales are no security risk to the U.S. He warns the measures will destroy jobs on both sides of the border.
In a statement to The Associated Press, the company said it views the tariffs with "regret and concern".
Dr Merkel said the measure "risks touching off spirals of escalation that in the end hurt everyone". "So it's not like the trade is imbalanced against the US favor on this".
In addition to Volkswagen vehicles, the company produces Audi, Porsche, and multiple other brands.
Canada's softwood lumber sector has been dealing with the latest USA tariffs to hit the industry for almost a year, handing over more than $200 million in 2017 to cover duties of about 20 per cent of the value of all exports.
The European Union on Friday formally set in motion its trade retaliation against the USA tariffs, filing a request for consultations at the WTO, which oversees disputes on global trade.
The riposte would be "firm" and "proportionate", and in line with WTO rules, Macron said. Throughout these talks, the USA has sought to use the threat of trade restrictions as leverage to obtain concessions from the EU.
Commerce Secretary Wilbur Ross said Thursday that the decision to slap Canada and Mexico with stiff steel and aluminum tariffs was based on a lack of progress in the NAFTA talks.