A 26-year-old law student in Austria is suing Facebook for breaching European privacy law in a class-action suit with 25,000 other users.
Max Schrems has filed his lawsuit in Vienna's Commercial Court this week, seeking injunctions against Facebook as well as damages of €500 (£396) per claimant.
Schrems claims that Facebook Ireland (a subsidiary of the New York-listed web giant) is in breach of European law on users' data and it violates rights by tracking internet use on external sites, including the use of 'like' buttons.
The claim also attacks Facebook's analysis of users through what it calls "big data systems" and claims the company supports the Prism surveillance programme, the US secret service's worldwide monitoring and data mining programme exposed by whistleblower Edward Snowden.
Schrems set up a website (fbclaim.com) that allows other users to join his claim, with him litigating on their behalf, but has had to limit the scale of the lawsuit today after being overwhelmed with support.
Around 7,000 users a day from more than 100 countries have registered backing Schrems' 'David v Goliath' legal challenge. At peak times since last Friday, a new user was joining the claim every six seconds, Schrems said.
The activist has announced that the case, which could be the largest class and privacy action ever taken, will be restricted to 25,000 Facebook members in order to verify each account.
"We have hoped for large support, but the number of participants in such a short time exceeded my most optimistic expectations", Schrem said.
Because the case is directed against Facebook's subsidiary in Ireland, it has broad European jurisdiction. A total of 944 UK members of the social networking site have signed up to back the case, though Germany tops the list of backers, with 5,287 Facebook users signing up there.
When numbers top 25,000, the Europe-V-Facebook.org campaign will continue to register the name and address of users who wish to join the action and they will be prioritised if the claim is expanded.
Schrem said: "With this number of participants, we have a great basis to stop complaining about privacy violations and actually do something about it. If we are successful, the outcome will, of course, have a positive impact on all users."
Facebook has several weeks to respond to the lawsuit, which will reach the European courts later this year.