President Donald Trump tweeted another tariff threat Friday, this time targeting imported autos from the European Union.

The president said on his feed that if the EU does not remove duties on U.S. cars, then the U.S. will have no choice but to act.

Trump tweet

The threat comes just two days after Commerce Secretary Wilbur Ross said no decision had been made on whether the U.S. would extend the volley of tariffs it has imposed on other goods to the automobile industry.

Trump's tweet rippled through the financial markets, sending shares of BMW, Volkswagen, Fiat Chrysler and Mercedes-maker Daimler all lower. Ford and General Motors shares also slipped following the news.

The 20 percent tariff actually would be a bit smaller than the 25 percent levy Trump had previously threatened. The president has railed against unfair tariffs slapped on U.S. goods in other countries and has vowed to reduce the trade deficit the country has with other nations, particularly China.

As part of tariffs expected to go online July 6, the administration has put a 25 percent tariff on Chinese goods including autos. China in turn has promised dollar-for-dollar retaliatory tariffs.

The auto tariffs are part of a broader strategy the White House has in which it has deemed duties on U.S. exports to be a threat to national security. Trump has directed the U.S. trade representative to find another $200 billion worth of Chinese imports for tariffs of 10 percent.