The lawsuit comes as Facebook's stock climbed Wednesday after a two-day decline. The stock rose 3.2 percent on the day to close at $32. That's still nearly 16 percent below the initial public offering price of $38.
The lawsuit, filed in U.S. District Court in New York, claims the company's IPO documents contained untrue statements and omitted important facts, such as a "severe reduction in revenue growth" that Facebook was experiencing at the time of the public offering. The suit's three plaintiffs claim they were damaged.
In a statement, Facebook said the lawsuit is without merit. Morgan Stanley declined to comment.
Meanwhile, a Senate panel said it was reviewing Facebook's high-profile stock offering last week amid allegations that the bank handling the IPO may have provided select clients with a negative assessment of the company.
A Democratic aide to the Senate Banking Committee says the panel wants to learn more about the initial public offering. The committee seeks briefings with representatives of Facebook, regulatory agencies and others. The aide spoke on condition of anonymity because the committee's planned inquiry hasn't been publicly announced.
Regulators are examining whether Morgan Stanley selectively informed clients of an analyst's negative view of Facebook's prospects before the stock offering.