What happened

Rivian Automotive (RIVN -3.88%) stock has been falling all year, entering this week down more than 70% year to date. Some of the recent drop may have been in anticipation of the expiration of the lockup period that occurred this weekend. After the electric vehicle (EV) maker's initial public offering (IPO) on Nov. 10, 2021, early investors were required to hold onto shares for a period of 180 days. But Rivian shares tumbled today on the first trading day after that expiration, down 16.6% as of 10:58 a.m. ET. 

So what

It wasn't just the lockup expiration that has investors selling this morning, though. Over the weekend, CNBC's David Faber reported that Ford will be selling some of its stake in Rivian. Ford was an early investor in Rivian, holding 102 million shares, or about 11%, in the company. Faber reported that Ford has lined up a sale of 8 million on those shares.

Rivian trucks lined up in parking lot.

Image source: Rivian Automotive.

Now what

Rivian shares went public at a price of $78 per share and more than doubled from there shortly after the IPO. But the stock closed Friday at just below $29. Ford sold the 8 million shares at $26.90 per share, according to the report. 

Ford reportedly still made a hefty profit on the shares it already sold, though, and that block of shares only represents about 8% of its holdings. It's not surprising that Ford wanted to raise some cash from the investment as it is working to ramp up its own electric vehicle production as it transitions from internal-combustion-powered cars and trucks. 

The report also identified another block of 13 million to 15 million shares that are being offered by an unknown seller, however. The news -- and flood of new shares on the market today -- has Rivian stock plunging today.