Two Facebook users claim that the site scans private correspondence between users for links to third-party website to share with advertisers.
Facebook has been hit with a class-action lawsuit alleging the social networking behemoth gleans data from purportedly private messages, in violation of users' rights.
Two plaintiffs claim the site scans private correspondence between users for links to third-party websites, sharing that information with the likes of "advertisers, marketers and other data aggregators".
The suit accuses Facebook of violating the Electronic Communications Privacy Act and California privacy laws.
Facebook has "systematically violated consumers' privacy by reading its users' personal, private Facebook messages without their consent", said the complaint, filed December 30 in the US District Court for Northern California.
"Representing to users that the content of Facebook messages is 'private' creates an especially profitable opportunity for Facebook, because users who believe they are communicating on a service free from surveillance are likely to reveal facts about themselves that they would not reveal had they known the content was being monitored," it said.
Asked for comment, Facebook said in a statement: "The allegations in this lawsuit have no merit and we will defend ourselves vigorously."
The suit was brought forth by two Facebook users from different US states, Matthew Campbell of Arkansas and Michael Hurley of Oregon.
It was filed on behalf of all US Facebook members who have used the site to send or receive a message that includes a link.
"Facebook scanned plaintiffs' messages and searched the website identified in the URL for purposes including but not limited to data mining and user profiling," the suit said.
According to the suit, Facebook earned $US2.7 billion ($A3.0 billion) from targeted advertising sales in 2011.
The suit also said that while Facebook hides the extent of its data mining from users, it is clear on the subject in its technical guidance for web developers.