What happened 

Shares of Nvidia (NASDAQ:NVDA), Facebook (NASDAQ:FB), Amazon (NASDAQ:AMZN), and Pinduoduo (NASDAQ:PDD) were all falling today on seemingly no company-specific news. Instead, the tech companies shed billions of dollars in total market cap value as the S&P 500 fell today. 

Nvidia was down by about 1%, Facebook slid by 1.4%, Amazon dropped 2%, and Pinduoduo plummeted by more than 10% as of 3:10 p.m. EDT.  

So what 

One of the biggest reasons these tech stocks fell today is likely because of a pullback in the broader market. The S&P 500 was down by about 1% as of this writing as investors reacted to a lot of negative news. 

Line and bar graphs on a dark red background.

Image source: Getty Images.

First up is the fact that the CDC reversed its indoor mask policy and now recommends that even people who have gotten their COVID-19 vaccines should wear masks again while in indoor public spaces, in some locations. 

The spread of the delta variant of the coronavirus is making investors worried that the U.S. economy will be hurt by pandemic-related restrictions. While the economy is bouncing back from 2020's lockdowns and social distancing, there's some fear that it's still unstable and new restrictions could slow its growth. 

And Nvidia investors may be concerned after some of the company's peers, including Intel and Texas Instruments, recently reported their quarterly financial results. Tech investors have been generally concerned about the semiconductor industry as the pandemic has disrupted the global supply for chips. 

Additionally, shares of Pinduoduo, an agriculture-focused technology platform company, may also be falling after the Chinese government has increased restrictions on China-based tech companies over the past few weeks. 

For example, the Chinese government threatened the ride-hailing company DiDi Global with unprecedented penalties or even delisting because it was unhappy with the company recently going public in the U.S. Shares of China-based tech stocks have fallen as a result. 

Now what 

It's very possible that shares of Nvidia, Facebook, Amazon, and Pinduoduo could face some more volatility in the near future. Both Facebook and Amazon will release their quarterly earnings reports this week, which, depending on what the companies report, could send their stocks up or down.

Additionally, tech investors are still trying to figure out where to put their money as the U.S. economy opens back up. Investors fled the tech sector earlier this year, only to jump back into the sector over the past few months. With new potential COVID-19 related restrictions coming to some cities, the stock market could be in for some more instability in the coming months. 

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.