Shake Shack files to sell 4 million shares, stock falls 5%

Shake Shack is offering 4 million new shares to investors, the burger chain disclosed in a regulatory filing after the market close on Monday.

Shares of Shake Shack were down 5% in after-hours trading following the news.

The stock was up 3% on Monday to close at $54.79.

Since its IPO in January, shares are up 19%.

At the completion of the IPO in February, the company sold 5.75 million shares at $21 per share.

This offering of Shake Shack shares is to sell shares held by existing holders, and it likely related to the end of the company's post-IPO lock up on July 29, the first chance many company insiders will have to unload their stake.

Here's the chart showing the after-hours decline in the stock.