The markets took another drubbing on Monday on worries that President Donald Trump’s protectionist trade rhetoric marked a dangerous foray into uncharted economic waters.

The Dow Jones plunged by almost 500 points on news that Trump was planning a crackdown on Chinese investment in U.S. technology firms. Traders worried that the president's efforts — nominally aimed at protecting intellectual property — would instead make America’s tech sector less attractive to innovators and investors. Aside from Boeing, several prominent technology stocks fell, including chipmaker Intel, plus Facebook, Amazon, Netflix, and Alphabet, parent company of Google.

“This is a little bit different because it involves investment. Tariffs on goods can be changed in a heartbeat,” said Michael O. Moore, a professor of economics and international affairs at George Washington University. “Investment is much more long-lived. If you restrict investments, that’s something that goes on for years or decades,” he said.

American technology companies have long resented the demands for intellectual-property sharing and joint ventures that are the cost of access to the lucrative Chinese market, but industry observers say the Trump administration is doing them no favors with its threat to curtail foreign investment from “countries that are trying to steal our technology,” according to a tweet Monday morning from Treasury Secretary Steven Mnuchin.

On behalf of @realDonaldTrump, the stories on investment restrictions in Bloomberg & WSJ are false, fake news. The leaker either doesn’t exist or know the subject very well. Statement will be out not specific to China, but to all countries that are trying to steal our technology. — Steven Mnuchin (@stevenmnuchin1) June 25, 2018

Mnuchin’s tweet came in the wake of reports from The Wall Street Journal and Bloomberg that the administration was planning restrictions on Chinese investment in American technology companies and on the exports of some American technologies to China.

“All possibilities that would better protect American technology, including potential changes to export controls, are under review,” Commerce Secretary Wilbur Ross told the Journal in a statement on Sunday.

Mnuchin’s Monday morning tweet pushed back against the notion that China was being singled out, but trade hardliners have taken aim in the past at Beijing’s sweeping Made in China 2025 initiative, a tech-forward policy lending government support to a number of key technology sectors that has rankled Washington and raised concerns about Chinese dominance in emerging technologies like robotics, aerospace and artificial intelligence.

“Certainly, we’ve seen U.S. tech companies getting frustrated with Chinese practices regarding partnerships and other forms of intellectual property transfer in China,” said Andrew Bartels, a vice president and principal analyst at Forrester Research. “On the other hand, I think a lot of U.S. tech companies still view China as a great opportunity,” he said, and commercial restrictions could have a chilling effect on American technological innovation and entrepreneurship.

More than 80 percent of good that American companies produce in China is sold within China, said Mary Lovely, a nonresident senior fellow at the Peterson Institute of International Economics and professor of economics at Syracuse University. “There are lots of American jobs that support those sales. Those are all being put at risk by this,” she said.

Long term, this could drive tech startups out of the United States entirely. Lovely pointed to news over the weekend that motorcycle manufacturer Harley-Davidson will move some of its production out of the United States to avoid tariffs. “The long-term cost is it will make it more unattractive to stay here, produce here and keep your headquarters” in the United States, she said.

Moore said that while China has been aggressive about the forced joint ventures and technology transfers, the pretext and the method — according to the Journal, investment restrictions would be issued under the purview of the International Emergency Economic Powers Act of 1977 — could easily backfire.

“I think that is a short-term strategy that has potentially very bad long-term consequences," he said.