The Electronic Privacy Information Center submitted the complaint on Thursday in which it said the social network had failed to inform
users that their personal information would be shared with researchers.

Earlier this week, Facebook acknowledged that it conducted a study of 7000,000 of its users’ emotions by tinkering with the number of positive and negative posts they saw in their news feeds. Researchers wanted to know how people would react and whether the tone would influence what they themselves posted on the social network.

At the time of the study in 2012, Facebook’s terms of service didn’t explicitly say that user data could be used for research studies. The company later updated its policy to include that possibility.

A complaint to the F.T.C., which polices whether companies adhere to their privacy policies, could trigger an investigation and eventual punishment. The agency has previously filed suit against Facebook for deceiving its users by publicly sharing personal information that many had thought was private. In a settlement, Facebook agreed to undergo annual privacy audits by a third-party and promised to refrain from making false privacy claims in the future.

A violation of that agreement could make the company subject to fines, although its unclear whether it applies in this case. The study took place before Facebook signed the agreement.

The United Kingdom’s data regulator is already investigating the matter.

Earlier this week, Sheryl Sandberg, Facebook’s chief operating officer, offered a sort of apology after a public uproar about the study. It was a familiar refrain for anyone who has heard Facebook executives apologize in the past following dust-ups over user privacy.

“It was poorly communicated,” Sandberg said while in New Delhi, according to WSJ. “And for that communication we apologize. We never meant to upset you.”

(This story was updated with additional information from the FTC complaint)