A data privacy campaigner has signed up 25,000 people to a "class action lawsuit" being taken against Facebook.
Max Schrems alleges that the way the social network monitors its members' activity on and off the site puts it in breach of EU laws.
As part of the claim, he also alleges that the company co-operated with Prism, a US surveillance scheme.
Facebook has previously denied knowing about Prism before it was mentioned in leaked US government documents.
The company has, however, acknowledged complying with national security requests from US government agencies.
Facebook has not commented on the wider case being brought against it.
The BBC understands it does not plan to respond until it has been served the relevant papers.
Mr Schrems asked Facebook users based outside the US and Canada who wished to take part in the case to sign up via an app.
Mr Schrems is demanding 500 euros ($667, £396) in damages for each of the first 25,000 people who signed up to the case.