Facebook, which also owns Instagram, and Twitter shut off the data access of Geofeedia, the Chicago-based data vendor that provided data to police, in response to the ACLU findings.
The report comes amid growing concerns among consumers and regulators about how online data is being used and how closely tech companies are cooperating with the government on surveillance, Reuters reported.
"These special data deals were allowing the police to sneak in through a side door and use these powerful platforms to track protesters," said Nicole Ozer, the ACLUs technology and civil liberties policy director.
The ACLU report found that as recently as July, Geofeedia touted its social media monitoring product as a tool to monitor protests. Geofeedia is a software platform that enables clients to monitor posts tied to a specific location.
The company said it aims to provide real-time, publicly available information to clients including corporations, media groups, cities and sports teams. Geofeedia is committed to the principles of personal privacy, transparency and individual rights and has clear policies to prevent the inappropriate use of its software, Chief Executive Officer Phil Harris said.
"That said, we understand, given the ever-changing nature of digital technology, that we must continue to work to build on these critical protections of civil rights," Harris said in an emailed statement.
Geofeedia works with over 500 law enforcement agencies and public safety agencies across the country, according to an email the ACLU obtained through a Freedom of Information Act request.
In a 2016 case study obtained by the ACLU, Geofeedia quoted Baltimore police Detective Sergeant Andrew Vaccaro who said the force intercepted kids with backpacks full of rocks after the Geofeedia team alerted them to chatter from a local high school.
Baltimore was swept by rioting in April 2015 following the funeral of Freddie Gray, a 25-year-old black man who died from a spinal injury after being arrested by police.
In an October 2015 email message, a Geofeedia employee touted its "great success" covering racially charged protests in the aftermath of the August 2014 shooting of black teenager Michael Brown by a white police officer in the St. Louis suburb of Ferguson.
Facebook and Instagram terminated Geofeedias access on Sept. 19, according to the ACLU.
"This developer only had access to data that people chose to make public," a Facebook spokesperson said in a statement. "Its access was subject to the limitations in our Platform Policy which outlines what we expect from developers that receive data using the Facebook Platform."
Facebooks platform policy says developers may not "sell, license, or purchase any data obtained from us or our services."
In a tweet, Twitter said that it was "immediately suspending Geofeedias commercial access to Twitter data," following the ACLU report.