The Information Commissioner's Office (ICO) is looking into whether Facebook broke data protection laws when it conducted a psychological study on users without their consent.
As we reported earlier this week the test saw Facebook control nearly 700,000 news feeds in order to reduce either negative or positive posts and then monitor how users responded.
The ICO, based in the UK, now says it plans to question Facebook over the study, while Facebook said it had taken "appropriate protections for people's information".
"We are happy to answer any questions regulators may have," Facebook's Richard Allen said in a statement as reported by various media outlets.
The Financial Times and The Register quoted the ICO as saying that it would contact Ireland's data protection regulator over the issue.
Facebook's European headquarters are based in Dublin.
Earlier this week the social media giant defended the research in a statement, writing: "This research was conducted for a single week in 2012 and none of the data used was associated with a specific person's Facebook account."
"We do research to improve our services and to make the content people see on Facebook as relevant and engaging as possible.
"A big part of this is understanding how people respond to different types of content, whether it's positive or negative in tone, news from friends, or information from pages they follow.
"We carefully consider what research we do and have a strong internal review process."
In the paper, the researchers, who were from Cornell University and the University of California at San Francisco, said the study "was consistent with Facebook's Data Use Policy, to which all users agree prior to creating an account on Facebook".
The full text of the study is available here.