Facebook, its founder Mark Zuckerberg, and the banks leading its flotation are being sued by disgruntled shareholders.
A writ filed in a Manhattan court says that Facebook's revised growth figures were not disclosed to all investors.
US financial regulators have already said Morgan Stanley may have questions to answer over the disclosure of information ahead of Friday's float, but the bank, which was the lead underwriter, says it fully complied with the rules.
The flotation on Friday was disrupted by technical glitches on the Nasdaq stock exchange.
The share price has since slumped amid worries that the company was over-valued by advisers marketing the float.
On Tuesday, a financial regulator in Massachusetts issued a subpoena to Morgan Stanley as part of an investigation into whether its analysts selectively disclosed revised revenue forecasts for Facebook.
Now, the BBC reports a group of investors has issued a class-action lawsuit alleging that Facebook revenues were revised down because of a surge in the number people using mobile devices for apps and connection to websites.
Morgan Stanley has not yet commented on the latest lawsuit.
However, Facebook shares were up 3.4% at $32 shortly after trading opened on Wall Street on Wednesday. The shares listed at $US38 per share and fell as low as $US31 on Tuesday.