By Jonathan Stempel

NEW YORK (Reuters) - Facebook Inc (FB.O) and the political consulting firm Cambridge Analytica have been sued in the United States for obtaining information belonging to 50 million of the social media company's users without permission.

The proposed class-action complaint filed late Tuesday night by Lauren Price, a Maryland resident, is the first of what could be many lawsuits seeking damages over Facebook's ability to protect user data, and Cambridge Analytica's exploitation of that data to benefit President Donald Trump's 2016 campaign.

"Every Facebook user has an interest in this lawsuit, and the enforcement of their privacy rights," John Yanchunis, a lawyer for Price, said in a phone interview on Wednesday.

The complaint was filed in the U.S. District Court in San Jose, California, several hours after Facebook was blamed in a shareholder lawsuit filed in nearby San Francisco for the drop in its stock price after the data harvesting was revealed. Nearly $50 billion of market value was wiped out in two days.

Facebook and Cambridge Analytica did not immediately respond on Wednesday to requests for comment.

Price accused Facebook and London-based Cambridge Analytica of negligence and violating a California unfair competition law.

She said the harvesting contravened Facebook's privacy policy, in which the Menlo Park, California-based company said user trust was "important to us" and that it would not share information without permission and notice.

"Our client saw a tremendous uptick in political messaging during the campaign on her Facebook page, which she had never seen," Yanchunis said. "She had a glimmer of understanding at the time, but now sees there was an attempt to influence her vote."

The complaint seeks unspecified damages, including possible punitive damages.

Yanchunis, who has also been suing Verizon Communications Inc (VZ.N) over data breaches at its Yahoo Internet business affecting 3 billion accounts, said it should be a "fairly easy exercise" to identify potential Facebook class members.

He said cybersecurity experts can assist with the case, and that Facebook "leaves a footprint of what was taken that cannot be erased."

The case is Price v Facebook Inc et al, U.S. District Court, Northern District of California, No. 18-01732. The shareholder case is Yuan v Facebook Inc et al in the same court, No. 18-01725.

(Reporting by Jonathan Stempel in New York; Additional reporting by Eric Auchard in London; Editing by Nick Zieminski)