United Airlines Inc. will have to face claims that it retaliated against an aviation technician who expressed concerns that the company was mishandling U.S. Air Force aircraft repairs.

United technician David Grant reasonably believed his employer was violating the False Claims Act when he informed his superiors that inspectors at the Charleston Air Force Base may have been certifying work that hadn’t been done, or had been done with “uncalibrated and uncertified tools,” the U.S. Court of Appeals for the...