Shares of technology companies slid as investors abruptly rotated out of the biggest winners from the coronavirus bull market.

"It's a combination of things: we had this incredible runup, so some stocks probably were due to fall anyway," said Joe Kinahan, chief market strategist at TD Ameritrade. "We still have questions with 'is there going to be a [fiscal] financing package or not?' Things seemed to look pretty good yesterday, then (Senate Majority Leader) Mitch McConnell threw a little bit of cold water on that ... and I think that makes people nervous, too."

Shares of electric carmaker Tesla compounded recent losses, retreating by 9% to close at $407, almost 20% below its highs Tuesday.

"Tesla's whole history has been volatile," said Mr. Kinahan. "They and Apple, leading up to the split, they had this incredible run."

Shares of other giants, including Apple, Facebook, Microsoft, Amazon.com and Google parent Alphabet were down by 3.5% or more. Facebook said it will prohibit new political advertisements in the week before the U.S. presidential election in November and seek to flag any candidates' premature claims of victory, Chief Executive Mark Zuckerberg said Thursday. Wall Street strategists have argued for weeks whether the improbable runup in these stocks, coming in the midst of a major recession, was a speculative bubble driven by a new generation of day traders -- the so-called Robinhood Markets crowd.

According to some observers, the trading app, which allowed bored, home-bound professionals to jump into the stock market and back hot stocks like the "mega cap" tech companies, has been a principal driver of one of the sharpest and unanticipated rallies in living memory.

Shares of "stay-at-home" stocks, companies whose business has picked up due to "remote working" trends, including videoconferencing app Zoom Video Technologies and digital-signature company DocuSign, were even harder hit.

Apple said it would delay until early next year a privacy change that would invite iPhone users to keep their devices cloaked from apps that want to track them, following complaints from Facebook and others that the move would thwart digital advertising sales.


 Write to Rob Curran at rob.curran@dowjones.com