Shake Shack falls as more shares will reach the market; investors are selling $240M in stock

Shake Shack stock declined about 9 percent Thursday after the burger chain said more of its shares will reach the market soon.

The "lock-up" period, when executives and key investors are barred from selling stocks after a company's initial public offering, has expired. Shack Shack first listed its shares in late January.

The new offering, which priced at $240 million, means a substantial boost in the number of available Shake Shack shares.

The company had 12.1 million Class A shares on the market as of Aug. 5, and Shake Shack said Wednesday that the investors are selling 4 million shares with an option to sell an additional 600,000 shares. The New York company won't get any proceeds from the sale, which is expected to close Tuesday.

The offering is priced at $60 per share, a 7 percent discount from Wednesday' closing price. Shares fell $5.99 to $58.80 in midday trading Thursday.

Shake Shack's IPO priced at $21 per share and the stock more than doubled in value on its first day of trading. The shares traded as high as $96.75 in May and slumped afterward, but they had rallied over the last month.