AT&T was sued by the Electronic Frontier Foundation today for selling customer location data to third parties, after controversy erupted earlier this year over wireless carriers’ data practices.

The digital activism group filed the proposed class action suit today on behalf of AT&T customers in California. The suit also named two other companies, LocationSmart and Zumigo, which have acted as data aggregators, collecting location information and selling it to third parties for commercial use.

“AT&T has knowingly breached its duties”

“AT&T has knowingly breached its duties to protect Plaintiffs’ sensitive location data in order to profit from it,” the suit reads.

The suit stems from recent investigations into how AT&T and other wireless carriers share the sensitive data. A New York Times article last year found that law enforcement has used the data to track phones without a court order. In another investigation, published earlier this year, Motherboard was able to pay a bounty hunter $300 to track the location of a phone using the data. Several lawmakers were quick to criticize the companies’ policies following the Motherboard report.

The Electronic Frontier Foundation, which is suing alongside the law firm Pierce Bainbridge, argues that the data, meant for tracking emergency calls, was not properly authorized by customers for commercial use. Calling AT&T’s practices “outrageous and harmful,” the suit argues that the sale of location data puts customers at risk, potentially exposing the information to people like stalkers.

Under federal law, the suit continues, AT&T is bound to secure the sensitive customer information, but has failed to do so. The suit also accuses the company of misrepresenting its privacy protections to customers.

“The facts don’t support this lawsuit, and we will fight it,” an AT&T spokesperson said in a statement. “Location-based services like roadside assistance, fraud protection, and medical device alerts have clear and even life-saving benefits. We only share location data with customer consent. We stopped sharing location data with aggregators after reports of misuse.”

The suit proposes to create a class of plaintiffs that includes AT&T customers living in California since 2011, and seeks damages for the customers, who number in the millions.

Update, 12:56PM ET: Includes statement from AT&T spokesperson.