President Donald Trump doubled down Friday night on his threat to order U.S. businesses out of China as part of an escalating trade war.

The president had tweeted on Friday morning, “We don’t need China and, frankly, would be far. ...better off without them. The vast amounts of money made and stolen by China from the United States, year after year, for decades, will and must STOP. Our great American companies are hereby ordered to immediately start looking for an alternative to China, including bringing... your companies HOME and making your products in the USA..”

After several leading economists publicly questioned whether Trump has the power to order private businesses to relocate, Trump lashed out at the news media.

“For all of the Fake News Reporters that don’t have a clue as to what the law is relative to Presidential powers, China, etc., try looking at the Emergency Economic Powers Act of 1977. Case closed!," he tweeted Friday night.

Jennifer Hillman, a Georgetown University law professor and trade expert at the Council on Foreign Relations, told The Washington Post that Trump does not have the power to order companies out of China, but he does have the authority under the International Emergency Economic Powers Act to prevent future transfers of funds to Beijing.

The International Emergency Economic Powers Act of 1977, approved by President Jimmy Carter, is part of the National Emergencies Act. It permits the president to block transactions and freeze assets in the events of an “unusual and extraordinary threat... to the national security, foreign policy, or economy of the United States.”

It was invoked by Carter during the Iran hostage crisis in 1977 and again by President George W. Bush following the 9/11 attacks in 2001 to freeze assets of terrorist organizations. It has also been used in response to events in such countries as Lebanon, Libya, Yemen and Venezuela.

Earlier this year, the White House said Trump might cite the act to impose tariffs on Mexican exports in response to illegal immigration into the U.S.

U.S. companies invested a total of $256 billion in China between 1990 and 2017, compared with $140 billion Chinese companies have invested in the U.S, according to the Rhodium Group research institute.