However, TheStreet's Debra Borchardt suggested the selling isn't all that bad when analyzed.
Zuckerberg plans to sell 41.4 million shares for an estimated $2.3 billion to pay taxes on a stock-option purchase of 60 million Class B shares, Borchardt said.
She said Zuckerberg's voting power would drop to 56.1% from 58.8%, which is still a rather sizable stake.
The secondary includes what Zuckerberg is selling plus 27 million shares from the company and 1.65 million shares from board member Marc Andreessen, she said.
Borchardt noted that FB will be added to the S&P 500 at the close of trading on Friday. Facebook shares are up over 100% in 2013.
-- Written by Bret Kenwell in Petoskey, Mich.