Many users were thoroughly freaked out earlier this year when it was revealed that Facebook had conducted a psychological experiment on some 700,000 users, affecting the content that showed up on their Newsfeeds to manipulate their emotions. At the time the news broke, the study was widely derided as being wrong and unethical. But now, according to two Maryland law professors, it also may have been downright illegal.

“What Facebook… did wasn’t just unethical. It was illegal,” said James Grimmelmann, a professor of law at the University of Maryland. “A common assumption is that even if research laws ought to apply to private companies, they don’t. But that assumption is false. Facebook… [is] bound by research laws, and those research laws quite clearly prohibit what they did.”

Grimmelmann and other another law professor at the University of Maryland, Leslie Metzer Henry, sent letters to both Facebook and OKCupid, which conducted a similar experiment.  Facebook responded and told him that the experiment was “research,” but Grimmelmann took apart the social media behemoth’s argument. He explained that, under Maryland law, research may not be conducted on human subjects without their consent, thus rendering their experiment against the law. Now it will be interesting to see if academics and experts in other states where the experiment took place will follow suit.