The Information Commissioner's Office said in a statement Wednesday that it wants to learn more about the circumstances of the experiment carried out by two U.S. universities and the social network.
The commissioner's office is working with authorities in Ireland, where Facebook has headquarters for its European operations. French authorities are also reviewing the matter.
The researchers manipulated the news feeds of about 700,000 randomly selected users to study the impact of "emotional contagion," or how emotional states are transferred to others. The researchers said the evidence showed that emotional contagion occurs without direct interaction between people and "in the complete absence of nonverbal cues."
Facebook acknowledged that the research was done for a single week in 2012.
"It's clear that people were upset by this study and we take responsibility for it," the company said in a statement. ". We want to do better in the future and are improving our process based on this feedback. The study was done with appropriate protections for people's information."
The concern comes amid interest in Europe about beefing up data protection rules. The European Court of Justice last month ruled that Google must respond to users' requests seeking to remove links to personal information.
Suzy Moat, a Warwick Business School assistant professor of behavioral science, said businesses regularly do studies on how to influence behavior. She cited the example of Facebook and Amazon experimenting with showing different groups of people slightly different versions of their websites to see if one is better than another at getting customers to buy products.
"On the other hand, it's extremely understandable that many people are upset that their behavior may have been manipulated for purely scientific purposes without their consent," Moat said. "In particular, Facebook's user base is so wide that everyone wonders if they were in the experiment."