Facebook Inc’s shares fell 4 percent in premarket on Monday after media reports that a political consultancy that worked on President Donald Trump’s campaign gained inappropriate access to data on 50 million Facebook users.

The move would knock $21.5 billion off the social network’s market value of $538 billion as of Friday’s close. One Wall Street analyst said the reports raised ‘systemic problems’ with Facebook’s business model and a number said it could spur far deeper regulatory scrutiny of the platform.

The head of European Parliament said on Monday that EU lawmakers will investigate whether the data misuse has taken place, adding the allegation is an unacceptable violation of citizens’ privacy rights.

Facebook was already facing new calls for regulation from U.S. Congress and questions about personal data safeguards after the reports from the New York Times and London’s Observer over the weekend.

The papers reported on Saturday that private information from more than 50 million Facebook users improperly ended up in the hands of data analytics firm Cambridge Analytica, and that the information had not been deleted despite Facebook demands dating back to 2015.

https://www.reuters.com/article/us-facebook-cambridge-analytica-stocks/facebook-shares-slide-after-reports-of-data-misuse-idUSKBN1GV1E8