The European Union estimates that the first wave of U.S. tariffs on steel and aluminum will hit up to €28 billion ($28.3 billion) worth of exports from the bloc, marking a major escalation in U.S. President Donald Trump’s trade war.

The amount of goods would be roughly four times larger than the last time Trump targeted Europe’s metals sector, according to Bloomberg News. After European Trade Commissioner Maros Sefcovic met his U.S. counterparts in Washington, he told the bloc’s ambassadors that the situation was fluid and the details and extent of any tariffs could still change, said the people, who asked not to be identified.

As part of his effort to shake up global trade rules, Trump has announced a series of tariffs including a 25 percent duty on steel and aluminum exports that could take effect on March 12. He also announced retaliatory tariffs based on partner policies that are seen as obstacles to U.S. trade.

The European Commission, which has authority over the EU’s trade moves, declined to comment. As for the EU, the dispute over U.S. metals tariffs began in 2018 during Trump’s first term, when the United States imposed duties on an estimated $7 billion worth of European steel and aluminum exports, citing national security concerns. Officials in Brussels at the time scoffed at the idea that the EU posed such a threat.

On Wednesday, European Trade Commissioner Maros Sefcovic said in Washington that the EU saw “no justification” for U.S. President Donald Trump to impose additional tariffs on its goods, but was prepared to respond “firmly and swiftly.”