Meta Platforms has been sued by patients saying Facebook was given access to their private medical data when they accessed web portals for some medical providers.

According to the lawsuit, filed as a proposed class action on behalf of millions of patients, Facebook’s pixel tracking tool secretly redirects secure information such as patient communications without user authorization, and in violation of state and federal laws.

The case is different from other accusations against Facebook, for gathering information on their own users, in that it is alleging Facebook was secretly stealing confidential data from two distant parties, while providing a service to a one party’s website or web portal.

The plaintiff was not identified. However he was referred to as a patient who used a Baltimore healthcare provider’s web portal to view lab results, make appointments, and communicate with his providers.

He seeks compensatory and punitive damages for breach of contract, violations of the Electronic Communications Privacy Act, and invasion of privacy, among other injuries.

The Markup, a non-profit news organization, revealed that 33 of Newsweek’s top 100 hospitals use Facebook’s Pixel on their appointment scheduling pages. The report noted that several of the identified hospitals have since removed the tracking software.

The lawsuit alleges it has identified at least 664 hospital systems or medical providers who use Pixel on their websites.

Meta has not commented on the lawsuit.

The case is John Doe v. Meta Platforms, 3:22-cv-3580, US District Court, Northern District of California (San Francisco).