In a separate statement released by the White House, Trump said he had "instructed" Ross to "consider" kicking off the probe. The EU adds 10 percent to the cost of imported American models, while the United States imposes a levy of 2.5 percent on most imported cars and 25 percent on most pickups.
The Department of Commerce will investigate the effect of vehicle imports under Section 232 of the Trade Expansion Act of 1962, which allows the president to restrict trade in the name of national security. The threat of tariffs could also be a useful bargaining chip, as the US tries to negotiate new trade agreements with Japan, Mexico, Canada, and the European Union.
"The Department of Commerce will conduct a thorough, fair, and transparent investigation into whether such imports are weakening our internal economy and may impair the national security".
The proposed import tax was seen as an additional pressure point in the negotiations, with Mexico and Canada already scheduled to lose their exemption from Trump's metals tariffs in little more than a week.
Both countries are part of the North American Free Trade Agreement (Nafta), which the Trump administrations wants to renegotiate in a bid to boost the United States manufacturing sector.
The Journal, citing sources in the auto industry, said U.S. moves to retaliate likely would face significant opposition from trading partners and auto dealers that sell imports.
By threatening a tariff on all imported cars, Mexico could be pressured into the tightening of the rules.
The tariffs on steel and aluminum imports followed a year-long investigation, so any action on auto imports could be months away.
In March, he threatened to hit European carmakers with tariffs if the European Union did not lower barriers to US vehicles.
Trump appeared to tease Wednesday's announcement with earlier tweets, saying: "There will be big news coming soon for our great American autoworkers".