The EU fired the shot across the U.S. bow after Trump said in an interview with ITV broadcast over the weekend that he has “a lot of problems with the European Union.” This “may morph into something very big” from “a trade standpoint,” he said.

The alert by the European Commission also follows Trump’s decision last week to impose tariffs on U.S. imports of solar panels and washing machines on the basis of rarely used “safeguard” rules. In addition, it comes amid a continuing threat by Washington to curb American purchases of foreign steel and aluminum on national-security grounds.

“The European Union stands ready to react swiftly and appropriately in case our exports are affected by any restrictive trade measures from the United States,” Margaritis Schinas, chief spokesman of the commission, the 28-nation EU’s executive arm, told reporters on Monday in Brussels. He declined to elaborate, saying his “point is better understood if I don’t.”