Wall Street shares plunged on Monday in a widespread sell-off led by technology companies.
Intel shares plummeted by more than 7% after a report that Apple plans to stop using Intel chips for computers.
E-commerce giant Amazon slid by more than 5%, after new attacks from US President Donald Trump.
The falls come amid increased debate in the US about competition and privacy rules, as well as tensions over trade.
The technology-heavy Nasdaq index lost more than 200 points, or almost 3%, by early afternoon.
The S&P 500 was down about 74 points or 2.8%, while the Dow fell more than 600 points or 2.6%.
Technology companies accounted for some of the steepest declines, but the falls touched every sector of the S&P 500 on a day with relatively light trading. European markets were closed.
Analysts said the sell-off reflected uncertainties affecting many aspects of the economy, including a rise in borrowing costs; debate about data regulations; and trade.
The US has imposed tariffs on steel and aluminium, prompting China this week to slap tariffs of up to 25% on certain goods worth $3bn from the US, including pork, fruit, nuts and wine.
Officials have also called for investigations of how companies handle consumer data, raising the possibility of stricter rules.
Fears of increased regulation are driving the decline in technology stocks, said Sucharita Kodali, a retail analyst for Forrester who tracks Amazon and other firms.
“The lack of regulation [in the US] has been fundamental to the success of these large tech companies … Their business is dependent on that,” she said. “That’s the fear.”
However, she said she thinks some of the panic is overblown, since any changes will take time to be implemented.
“It’s just so speculative,” she said.
Monday’s declines come amid weeks of choppy market trading, which have unsettled investors after the calm upward glide last year.
Investors had specific reasons to dump certain stocks on Monday.
Bloomberg reported that Apple is developing its own chips to use in its computers, with the transition planned as soon as 2020, triggering the plunge in Intel shares.
Tesla shares also fell by more than 5%, after the firm was rebuked by US safety regulators for sharing information about a recent crash. Investors are also worried about the company’s finances, as it spends heavily to ramp up car production.