Public posts on Twitter, Facebook and Instagram have been monitored by a company called Geofeedia. It has been giving user data to police.
The American Civil Liberties Union of California discovered the surveillance through public records. Emails say Baltimore Police used Geofeedia to "stay one step ahead of rioters" after the death of Freddie Gray.
Now the three social media sites are shutting down the company's access to their public posts.
Geofeedia issued a notice saying that they're committed to "free speech and civil liberties."