SAN FRANCISCO ­– A federal magistrate judge on Thursday sanctioned a law firm for publicly filing documents containing Grubhub Inc.'s confidential information in a lawsuit claiming the delivery service misclassified workers as contractors.

“I'm going to grant the motion for sanctions,” U.S. Magistrate Judge Jacqueline Corley of the Northern District of California said at a hearing. “It was absolutely inexcusable to do that filing without redacting that information.”

Boston labor law firm Lichten & Liss-Riordan will have to pay Grubhub at least $15,000 to cover legal fees the company incurred in responding to the breach, Corley said. Grubhub is represented by a team of lawyers at Gibson, Dunn & Crutcher led by partner Theodore Boutrous Jr.