President Trump on Friday threatened to unilaterally impose a 20 percent tariff on all automobile imports from Europe, further breaking from Republicans in Congress and front-running an investigation he had ordered from the Commerce Department into whether these imports harm the U.S.’s national security.

It was the first time he had threatened to impose a specific level of tariffs on automobiles from Europe.

The tweet came as Europe imposed tariffs on goods worth $3.2 billion) – including Harley Davidson motorcycles and Levi’s jeans – which are themselves a targeted response to Trump’s earlier decision to impose steel and aluminum tariffs on European exports to the United States.

Trump and Peter Navarro, one of his top trade advisers, have long believed that the European Union has an unfair tariff on U.S. exports while the U.S. government makes it relatively easy for other countries to send their cars here.

The EU charges a 10 percent tariff on auto imports from the United States. Trump is threatening to impose a tariff double that size if the EU doesn’t remove its barriers.

Trump had a messy showdown with leaders from Europe and Canada at a recent Group of Seven meeting. French leader Emmanuel Macron has accused Trump of being protectionist and isolationist, and Trump has had a chilly relationship with German Chancellor Angela Merkel.

Germany is the largest European manufacturer of automobiles, though German companies have a huge presence in the United States, with large factories in South Carolina and Tennessee.

It is difficult for the White House to unilaterally impose tariffs without input from Congress, but Trump has found several ways to do it this year. Several weeks ago, he ordered Commerce Secretary Wilbur Ross to launch what’s known as a “232” investigation. If this investigation finds that the “national security” of the United States is compromised by a reliance on imports, than tariffs can be imposed.