(CBS SF) — A consumer privacy group has filed a complaint with the Federal Trade Commission accusing Facebook of breaking the law when it performed a psychological experiment of its users without their knowledge or consent.

The Electronic Privacy Information Center filed the complaint on Thursday, calling the study a deceptive trade practice.

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“At the time of the experiment, Facebook did not state in the Data Use Policy that user data would be used for research purposes. Facebook also failed to inform users that their personal information would be shared with researchers,” the complaint says.

Facebook responded saying it has since adopted stricter standards for reviewing studies.

“When someone signs up for Facebook, we’ve always asked permission to use their information to provide and enhance the services we offer,” Facebook spokeswoman Jodi Seth told the New York Times on Thursday. “To suggest we conducted any corporate research without permission is complete fiction. Companies that want to improve their services use the information their customers provide, whether their privacy policy uses the word ‘research’ or not.”

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On Wednesday, Facebook’s Chief Operating Officer Sheryl Sandberg said the move was “poorly communicated” and that companies do what Facebook did all the time.

“This was part of ongoing research companies do to test different products, and that was what it was; it was poorly communicated,” Sandberg told the Wall Street Journal. “And for that communication we apologize. We never meant to upset you.”

The Menlo Park-based company conducted a one-week study in 2012 to see if they could influence user mood by altering news feeds.

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Employees tweaked the visible content for nearly 700,000 users to provide them with either upbeat posts or primarily negative news. The company then monitored subsequent posts to see how positive or negative the studied user’s posts were.