The European Commission (EC) has angrily reacted to news that the United States will impose steel and aluminum tariffs on Canada, Mexico and the European Union (EU).

U.S. Commerce Secretary Wilbur Ross announced at a news briefing Thursday that tariffs of 25 percent on steel imports and 10 percent on aluminum imports will take effect from midnight.

In a tweet following the news, the EC said: “The EU believes these unilateral U.S. tariffs are unjustified and at odds with World Trade Organization rules. This is protectionism, pure and simple.”

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In a press release, EC President Jean-Claude Juncker said the EU was being hurt as much as the U.S. by overcapacity in the steel sector.

He added that the U.S. was “playing into the hands of those responsible for the problem” and that the EU now had no choice but to proceed with legal challenge via the World Trade Organization (WTO).

“We will defend the Union’s interests, in full compliance with international trade law,” said Juncker.

Prior to the announcement, German Chancellor Angela Merkel told reporters the tariffs would be incompatible with WTO rules and that Europe’s response must be “smart and determined.”

French Finance Minister Bruno Le Maire also said Thursday that Europe would take “all necessary measures” to respond. The EU had previously said it would impose its own tariffs on U.S. products such as motorcycles and jeans.

German Finance Minister Olaf Scholz said in an interview with Reuters on Thursday that the EU’s response to the tariffs must be “clear, strong, and smart.”

When asked if there were any signs that the trade dispute could be resolved, Scholz added: “No, there are no such signs.”

Metal producers in the countries affected had been granted a temporary exemption from the tariffs after they were introduced earlier this year; this exemption had been due to expire Friday.

The tariffs were originally announced on March 1 when President Donald Trump said that the United States was being treated unfairly.

“People have no idea how badly our country has been treated by other countries. By people representing us who didn’t have a clue,” Trump said, arguing that trade trends “destroyed” American steel and aluminum industries.