Last updated: 1:49 p.m. PT.

Facebook shareholders have sued the social network, CEO Mark Zuckerberg, and a number of banks, alleging that crucial information was concealed ahead of Facebook's IPO.

The lawsuit, filed in the U.S. District Court in Manhattan this morning, charges the defendants with failing to disclose in the critical days leading up to Friday's initial public offering "a severe and pronounced reduction" in forecasts for Facebook's revenue growth, as users more and more access Facebook through mobile devices, according to Reuters, which cited a law firm for the plaintiffs. (The case: Brian Roffe Profit Sharing Plan v. Facebook, 12-04081.)

Earlier this month, Facebook updated its filings with the Securities and Exchange Commission to say that the shift to smartphones and other mobile gadgets is cutting into the prices it can set for advertisers, which would in turn hurt the company's revenue. In March, the social network had 488 million monthly average unique users of its mobile products, out of a total of just over 900 million registered users.

The plaintiffs charge that the changes to the forecast by several underwriters of the IPO were only "selectively disclosed" to a small group of preferred investors and not to the investment community at large. "The value of Facebook common stock has declined substantially and plaintiffs and the class have sustained damages as a result," the complaint says, per the Reuters report.

Facebook's stock opened Friday priced at $38 and, aside from a slight uptick right at the start, has been trading lower since then. It closed at $31 last night. In early trading today, shares were up better than 3 percent, even with word of the lawsuit -- and at the end of the day, that's where they closed, at $32 even..

In response to the legal action, a Facebook spokesperson said, "We believe the lawsuit is without merit and will defend ourselves vigorously."

A report from well-known Wall Street watcher Henry Blodget, citing an unnamed source, posits that a Facebook executive was responsible for telling institutional investors, but not smaller investors, about the reduction in revenue estimates.

Speaking on CBS This Morning today, Blodget described the sequence of events regarding the estimates and the failure to fully share material information. "The fact that it was only distributed verbally to a handful of institutions as opposed to all investors is a problem," he said.



The issue may already be well on its way to becoming a political one, too. Sen. Sherrod Brown (D-Ohio), chairman of the Senate Banking Subcommittee on Financial Institutions and Consumer Protection, later in the day issued a statement via e-mail expressing concern about the possibility that some of Facebook's financial details might not have been shared widely enough.

"Effective capital markets require transparency and accountability, not one set of rules for insiders and another for the rest of us. There's a lot that we don't know about this IPO but a lot that we do," Brown said in the statement. "We know that the SEC must fully investigate and take appropriate action if it discovers any violations."

This isn't the only lawsuit related to Facebook's IPO. A Maryland investor, for instance, is suing the Nasdaq stock exchange over glitches in how it handled the offering.

Editors' note: This story was updated several times throughout the day with additional information, including the statement by Sen. Sherrod Brown, Facebook's response to the lawsuit, and the closing price for Facebook shares.

Henry Blodget on CBS This Morning: