The filing was made this week by an unidentified individual and the case has been assigned to the agency's New York office, according to the agency's website. It involved an alleged violation of a New Deal-era ban on punishing employees for involvement in collective action related to working conditions, according to a case summary posted online. An attorney listed as representing the complainant didn't immediately comment in response to an inquiry.

It's unclear who the complainant is. Over the past year, staff have protested over workers' rights, a divisive military contract and the company's handling of sexual misconduct. Tens of thousands of Google employees around the world participated in a November walkout, demanding changes. The company's since addressed some of the organizers' demands, announcing it would let employees pursue claims as class actions in court rather than forcing them into arbitration.

This week, the internet giant came under fire from two leaders of the walkout, who alleged in a message posted internally that the company has been retaliating against them -- a claim Google has denied. The activists, whose message was first reported by Wired, announced a planned town-hall meeting on the issue Friday.