Meta has made so called “end-to-end” encryption a central part of WhatsApp’s feature set, offering a kind of encryption that means a message is only accessible to the sender and recipient, but not the company.

In this kind of encrypted chat, which the company says is turned on by default, WhatsApp’s in-app messaging says “only people in this chat can read, listen to, or share” the messages.

In the lawsuit filed Friday in US District Court in San Francisco, the group of plaintiffs allege that Meta’s privacy claims are false. They allege that Meta and WhatsApp “store, analyze, and can access virtually all of WhatsApp users’ purportedly ‘private’ communications” — and accuse the companies and their leaders of defrauding WhatsApp’s billions of users worldwide.

A spokesperson for Meta, which acquired WhatsApp in 2014, called the lawsuit “frivolous” and said that the company “will pursue sanctions against plaintiffs’ counsel.”

“Any claim that people’s WhatsApp messages are not encrypted is categorically false and absurd,” spokesperson Andy Stone said in an email. “WhatsApp has been end-to-end encrypted using the Signal protocol for a decade. This lawsuit is a frivolous work of fiction.”

The group, which includes plaintiffs from Australia, Brazil, India, Mexico and South Africa, alleges that Meta stores the substance of users’ communications and that workers can get access to them.

The complaint cites “whistleblowers” as having helped bring this information to light, though it doesn’t explain who they are.

Lawyers for the plaintiffs are asking the court to certify a class-action suit. Multiple attorneys listed in the suit from the firms of Quinn Emanuel Urquhart & Sullivan and Keller Postman didn’t immediately respond to requests for comment. Another one of the plaintiff’s lawyers, Jay Barnett, from Barnett Legal, declined to comment Saturday night.