Two US government panels are to investigate Facebook's high-profile stock offering amid claims that the bank handling the flotation may have provided only select clients with a negative assessment of the company.
South Dakota Democrat Tim Johnson, chairman of the Senate Banking Committee, said that his panel wanted to learn more about the offering.
The social network began trading publicly on Friday.
The committee is seeking briefings with Facebook representatives, regulatory agencies and others.
After the briefings, Mr Johnson will determine whether a hearing should be held.
The House of Representatives Financial Services Committee is also is gathering information about Facebook's IPO (initial public offering). The committee staff was receiving briefings, an aide to the panel said.
The subject is likely to be raised in hearings by the Financial Services Committee in the coming weeks, even though no hearings are planned specifically on the Facebook IPO, the aide said.
Facebook began trading publicly on Friday on the Nasdaq.
Senator Sherrod Brown, a senior member of the Senate banking panel, said well-functioning securities markets "require transparency and accountability, not one set of rules for insiders and another for the rest of us". "We know that the (Securities and Exchange Commission) must fully investigate and take appropriate action if it discovers any violations," he said in a statement.
Regulators are examining whether Morgan Stanley, the lead underwriter for the IPO, selectively informed clients of an analyst's negative view of Facebook's prospects before the stock offering. In addition, several shareholders have sued Facebook and Morgan Stanley, claiming the IPO documents contained false statements and omitted important facts.