The Federal Trade Commission is investigating Facebook's privacy practices following a week of privacy scandals including allegations a Trump-affiliated political consulting firm got data inappropriately from millions of Facebook users.
The rare announcement sent Facebook's stock tumbling - at one point Monday morning down more than 6 percent - as the company faced potential new punishment by the US government, including fines that could reach well into the millions of dollars.
In a statement to CNBC, Rob Sherman, deputy chief privacy officer for Facebook, said Facebook remains "strongly committed to protecting people's information", and appreciates "the opportunity to answer questions the FTC may have".
"The FTC takes very seriously recent press reports raising substantial concerns about the privacy practices of Facebook", said Tom Pahl, acting director of the FTC's Bureau of Consumer Protection.
Facebook is getting another dose of bad headlines in regard to privacy, amid revelations that the company has been storing data about Android users' phone calls and text messages. Facebook is now facing the possibility of being fined with an amount that could reach billions of dollars if the FTC finds the company broke the terms of the decree.
The Cambridge Analytica scandal emerged only a few months before a landmark European Union data protection law comes into force under which companies found to be in breach could be fined up to 4 percent of global turnover.
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Barley said Facebook reacted "favorably" to her demand for greater transparency about the algorithms that underpin the company's data collection.
Last week, the House of Representatives Energy and Commerce Committee formally invited Zuckerberg to testify and the Senate Commerce Committee also invited him to appear. He says the hearing also will examine what steps companies like Facebook can do to better protect personal information. He also said sorry in full-page advertisements in British and US newspapers.
His apologies have failed to quell discontent.
Facebook was in the midst of dealing with that outcry, including promises from CEO Mark Zuckerberg to perform a full audit of anybody who might have extracted personal data using the old, since-tightened APIs.
Advertisers and users are also unhappy.
Opinion polls published on Sunday in the United States and Germany cast doubt over the trust people have in Facebook.
Fewer than half of Americans trust Facebook to obey US privacy laws, according to a Reuters/Ipsos poll released on Sunday, while a survey published by Bild am Sonntag, Germany's largest-selling Sunday paper, found 60 percent of Germans fear that Facebook and other social networks are having a negative impact on democracy.