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Facebook said the lawsuit "has no merit."
Matt Campbell, author of the left-leaning muckraking site the Blue Hog Report, filed a class-action complaint on Monday in the U.S. District Court for the Northern District of California.
Campbell is suing the tech giant alongside co-plaintiff Michael Hurley, an Oregon resident who was unavailable for comment.
The core of their complaint concerns the access advertisers have to messages. From the complaint:
Contrary to its representations, "private" Facebook messages are systematically intercepted by the Company in an effort to learn the contents of the users' communications... This practice...enables Facebook to mine user data and profit from those data by sharing them with third parties - namely, advertisers, marketers, and other data aggregators.
A Facebook spokesperson told Business Insider, "We continue to believe the allegations in this lawsuit have no merit and we will defend ourselves vigorously."
Campbell and Hurley's case is essentially based on Facebook's perceived lack of transparency regarding the tally of a company's "likes" on its network.
An advertiser can only send ads to a user if that user has some connection to the brand in question. A connection can include group membership or a "like" of that brand's corporate page.
And while it is made clear to developers and marketers, many Facebook users may not realize that a brand's "like" tally is based on direct clicks of the "like" button on that page, shares of a link directed to one of that brand's sites, and each "like" of one of those shared links.
Hacker News revealed back in Oct. 2012 that a shared link within a private message between Facebook users also counts toward the total. Facebook admitted this to the Wall Street Journal in that publication's follow-up story. In that same response, Facebook said that "absolutely no private information has been exposed." Users can create as many likes as they want by sending links in messages, even if they don't actually like a page.
Now, Campbell and Hurley are accusing Facebook of invading users' privacy by reading personal messages without their consent.
This past October, Campbell sued Arkansas Lt. Gov. Mark Darr for violating the Freedom of Information Act when he refused to release his personal cell phone number in response to an open records request.
Campbell previously used his blog to point out problems in Darr's campaign finance records, highlighting illegal funding and dubious expenses. Darr ended his congressional bid after just 17 days due to the controversy Campbell's report created.
Campbell and Hurley are asking the court to make Facebook change its policy of scanning links from private messages, and give a monetary award for users whose messages were scanned.