EU chief Ursula von der Leyen vowed on Tuesday to retaliate firmly against US President Donald Trump's decision to impose tariffs on steel and aluminium imports.
German Chancellor Olaf Scholz also said the European Union would present a united front and "act together as the largest market in the world".
Trump signed executive orders to impose 25 percent tariffs on steel and aluminium imports from March 12, despite warnings from Europe and China.
"I deeply regret the US decision to impose tariffs on European steel and aluminium exports," European Commission president von der Leyen said in a statement.
"Unjustified tariffs on the EU will not go unanswered -- they will trigger firm and proportionate countermeasures. The EU will act to safeguard its economic interests. We will protect our workers, businesses and consumers," she added.
EU trade chief Maros Sefcovic said it was "a lose–lose scenario", warning that tariffs were "economically counterproductive".
"By imposing tariffs, the US will be taxing its own citizens, raising costs for its own business, and fuelling inflation," he told the EU parliament in Strasbourg, France.
In one executive order, Trump said: "As of March 12, 2025, all imports of aluminum articles and derivative aluminium articles from Argentina, Australia, Canada, Mexico, EU countries, and the UK shall be subject to the additional ad valorem tariff."
He issued a separate order for steel, which said it would apply to all imports from the same countries the aluminium tariffs hit, as well as to Brazil, Japan and South Korea.
The US president indicated further additional customs duties could be on the way for cars, pharmaceuticals and computer chips.
His latest orders will feel like deja vu for Europe.
In 2018, Trump slapped tariffs during his first presidency on steel and aluminium exports -- forcing the EU to respond with its own higher duties.
The American Chamber of Commerce to the EU also said on Tuesday that it opposed Trump's decision, warning it would "have a wide-reaching and overwhelmingly negative impact on jobs, prosperity and security on both sides of the Atlantic".