Facebook has two types of stock. Class A and Class B. Class B stock gets 10 votes per share, while Class A stock gets 1 vote.
Zuckerberg and other very early people had Class B stock so they can continue to have more than 50% of the vote even when they own less than 50% of the stock.
This was a really popular stock structure in Silicon Valley for a while because it cements founders in control - Evan Siegel at Snap has the same deal, and Adam Neumann at WeWork was about to do it. But now there's a lot of push back against it, and some indexes like the S&P 500 refuse to list new stocks with this dual class structure.
Note that the S%P doesn't have the power to delist stocks. They can drop them from their index (which certainly would cause some reputational harm and probably lower the stock price a bit, at least temporarily), but FB will continue to trade on Nasdaq.
Zuckerberg and other very early people had Class B stock so they can continue to have more than 50% of the vote even when they own less than 50% of the stock.
This was a really popular stock structure in Silicon Valley for a while because it cements founders in control - Evan Siegel at Snap has the same deal, and Adam Neumann at WeWork was about to do it. But now there's a lot of push back against it, and some indexes like the S&P 500 refuse to list new stocks with this dual class structure.