WASHINGTON (AP) — President Donald Trump is threatening to slap a 20 percent tariff on cars from the European Union.

In a tweet Friday, Trump complains about EU trade barriers and vowed "if these Tariffs and Barriers are not soon broken down and removed, we will be placing a 20% Tariff on all of their cars coming into the U.S. Build them here!"

The EU has just slapped tariffs on $3.4 billion in U.S. products, ranging from bourbon to motorcycles, in retaliation for Trump's decision to tax imported steel and tariffs.

Trump has already directed U.S. trade officials to study whether auto imports pose a threat to national security that would justify hitting them with tariffs or quotas.