Less than two hours after President Donald Trump's tariffs on steel and aluminum took effect early Wednesday, the European Union retaliated with countermeasures worth around $28 billion on U.S. exports to the bloc.

It was the latest escalation in the global trade turmoil triggered by Trump's campaign to use tariffs as a tool to put pressure on friends and foes alike. He has appeared undeterred by the uncertainty and fear it has injected into the global economy, and has not ruled out the possibility that his policies would cause a recession in the United States.

The 25% tariffs on the import of steel and aluminum have the support of domestic producers. But they could hit a range of industries, including car manufacturing, and potentially slow down the U.S. economy.

Trump issued tariffs on Canada, Mexico and China last week, before quickly walking some of them back. Countries hit by the tariffs have vowed to retaliate with their own penalties, which will most likely hurt U.S. exporters.

Metal suppliers: The latest tariffs will hit producers across several continents. Canada is the largest supplier of steel and aluminum to the United States. Brazil, Mexico, South Korea and Vietnam are among the top suppliers of steel, while the United Arab Emirates, Russia and China are leading sources of aluminum.

Spooked markets: Stocks in Asia on Wednesday slightly moderated after a volatile day of trading, though shares in Australia fell for a second day. Shares of some big automakers, including Ford and Stellantis, have suffered losses this week.

Economic impact: More tariffs could be on the way. Trump has threatened to impose penalties on foreign cars and other "unfair" relationships, as part of an effort to force companies to bring manufacturing back to the United States.

This article originally appeared in The New York Times.