Facebook is in trouble for its privacy practices yet again. This time the Electronic Privacy Information Center (EPIC), a privacy watchdog group, has filed an official complaint against the social network for its 2012 emoticon study. Writing on The Wall Street Journal’s Bits blog, Brian R. Fitzgerald reports that the complaint states that Facebook Inc (NASDAQ:FB) didn’t obtain the consent of users before conducting the study.

Facebook Emotional Manipulation

Facebook users were guinea pigs

Last weekend, details about Facebook’s psychological study started making rounds through social media. The social network reportedly altered almost 700,000 users’ News Feeds to make them show either more positive or more negative posts. The study revealed that those who were exposed to more positive content were more likely to create positive posts, while those who saw more negative posts were more likely to create negative posts.

EPIC said Facebook did not say in its data use policy that it would use the information about its users for research purposes. At the time of the experiment, Facebook’s September 2011 Data Use Policy was reportedly in effect, according to the group’s complaint.” Four months later, the social network added language about “internal operations, including troubleshooting, data analysis, testing, research and service improvement” to its Data Use policy, according to the complaint.

The privacy group also said that the social network “purposefully messed with people’s minds.” The group also states that Facebook’s study was a “deceptive trade practice.” It calls for the FTC to place sanctions on Facebook and force it to publish the algorithm that’s in control of what people see in their News Feeds.

Facebook defends the study

This past week, the social network said it has always asked for consent from its users to use the data it collects to make improvements to its services. Executives said giving permission to use data to improve its services also extends to being able to conduct research on its users. They said it does not matter if the word “research” is used in asking for consent to use their information.

Facebook already faces an investigation in the U.K. from data protection regulators in Ireland.