An attorney representing Facebook users on Wednesday asked a federal judge to certify a class action against the social network over what he called its “continued systematic harvesting of private message content.”

Class attorney Michael Sobol said during Wednesday’s hearing that “extensive and rather contentious and hard-fought discovery” has led plaintiffs to believe that Facebook’s source code is designed so that private messages between users are scanned for content that can then be used for advertising purposes, Courthouse News Service reported.

“Every time a private message is sent with a URL attachment, Facebook intercepts it, analyzes it and creates a user-specific data structure out of the content of the private message,” Mr. Sobol told U.S. District Judge Phyllis Hamilton, according to the website.

“They have all this stuff sucked up in a vast database,” he added. “There needs to be a limitation here on what they’re exploiting under promises of privacy.”

The suit was first brought on behalf of Facebook user Matthew Campbell in 2013, who alleged violations of the federal Electronic Communications Privacy Act, as well as California’s Invasion of Privacy Act and section 17200 of California’s Business and Professions Code. Three years later, attorneys for the plaintiffs are asking Judge Hamilton to certify a class of Facebook users who can join the suit, potentially opening up the case to millions of account holders who have communicated over the platform.

“Frankly, this case is about no less than the future of privacy on the Internet,” Courthouse News quoted Mr. Sobol as saying.

On Facebook’s part, attorney Christopher Chorba argued “this case is ill-suited for class treatment because there are a number of individualized issues necessary to resolve plaintiffs’ claims,” the website reported.

“Unless we brought everyone through here, we couldn’t possibly know” whether they had consented to having their messages scanned, Facebook’s attorney added, according to The Recorder.

Companies are exempted from liability under the ECPA only if the sender or receiver have consented to interception, The Recorder Facebook-Fights-Class-Cert-in-LinkScanning-Suit?mcode=0&curindex=0&curpage=ALL”>noted.