Breaking News Emails

Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.
 / Updated  / Source: Reuters

WASHINGTON — President Donald Trump kept up pressure on trading partners on Saturday, threatening European automakers with a tax on imports if the European Union retaliates against his plan to slap tariffs on aluminum and steel.

Trump's tweet showed he is refusing to yield to U.S. business interests and foreign trading partners alarmed at the prospect of a trade war that rattled financial markets this week.

"If the E.U. wants to further increase their already massive tariffs and barriers on U.S. companies doing business there, we will simply apply a Tax on their Cars which freely pour into the U.S.," Trump wrote on Twitter. "They make it impossible for our cars (and more) to sell there. Big trade imbalance!"

Trump's threat comes amid mounting transatlantic tension on trade.

On Thursday, Trump said the United States would apply duties of 25 percent on imported steel and 10 percent on aluminum to protect domestic producers.

Related: Trump was angry and 'unglued' when he started a trade war, officials say

The next day, European Commission President Jean-Claude Juncker told German television that "We will put tariffs on Harley-Davidson (motorcycles), on bourbon and on blue jeans — Levis."

Canada also has said it will retaliate for any tariffs on steel and aluminum.

Trump had tweeted on Friday that trade wars are good and "easy to win," roiling U.S. financial markets.

Related: Trump administration wrong on tariffs and trade wars, experts say

In January 2017, Trump warned German car companies he would impose a border tax of 35 percent on vehicles imported to the U.S. market.