America’s biggest allies and trade partners are promising to fight back against US tariffs that threaten to spark a global trade war.

The European Union, Canada and Mexico said Thursday that they will respond to new US tariffs on steel and aluminum with punitive measures targeting American products worth billions of dollars.

Jean-Claude Juncker, president of the European Commission, said the bloc would move ahead with tariffs that are expected to affect roughly $7.5 billion worth of US exports. It will also lodge a case with the World Trade Organization (WTO).

Chrystia Freeland, Canada’s Minister of Foreign Affairs, outlined the country’s retaliation plan on Thursday. She said that Canada will place tariffs on American goods, including steel and aluminum. Some products will be taxed 10% and others 25%.

During a press conference, Freeland called the retaliation "the strongest trade action Canada has taken in the post-war era."

"Let me be clear," Canadian Prime Minister Justin Trudeau said. "[The US] tariffs are totally unacceptable."

The Mexican government said that the US action was not justified, and that it would retaliate with its own comparable penalties on US products including lamps, pork, fruit, cheese and flat steel.

The new US tariffs on steel and aluminum are set to go into effect on Friday.