A Twitter message purporting to come from the Anonymous hacker collective says the group's planning to destroy Facebook on November 5th.
The group claims that Facebook has been providing information to governments, and describes it as 'the opposite of the Antisec cause'.
"Facebook has been selling information to government agencies and giving clandestine access to information security firms so that they can spy on people from all around the world," says the group in an associated YouTube video.
"Some of these so-called whitehat infosec firms are working for authoritarian governments, such as those of Egypt and Syria."
It's something that Facebook has always denied, saying it doesn't share information with any third parties unless the user has agreed.
The group is also upset about Facebook's much-criticized privacy policies.
"Everything you do on Facebook stays on Facebook regardless of your 'privacy' settings, and deleting your account is impossible, even if you "delete" your account, all your personal info stays on Facebook and can be recovered at any time," it says.
"Changing the privacy settings to make your Facebook account more 'private' is also a delusion. Facebook knows more about you than your family."
The group doesn't make it clear exactly what it plans to do, although a DDoS attack would seem most likely. Bringing down the site could be enormously unpopular with users - indeed, it doesn't seem to be that popular with other members of Anonymous.
"FYI - #OpFacebook is being organised by some Anons. This does not necessarily mean that all of #Anonymous agrees with it," says Anonops on a Twitter feed associated with the group.
The date of November 5th - known in the UK as Bonfire Night - is significant. It was on this day in 1605 that Guy Fawkes and his fellow-conspirators planned to blow up the British Houses of Parliament. It's worth remembering, though, that they failed.