A lawyer bringing a gender discrimination class action against Microsoft Corp. faced tough questions Monday from a federal appeals court panel struggling to understand the process by which the software giant determined its pay and promotions.

Anne Shaver, a partner at San Francisco’s Lieff Cabraser Heimann & Bernstein, tried to convince the U.S. Court of Appeals for the Ninth Circuit to reinstate a nationwide class action alleging Microsoft systematically discriminated against more than 8,600 female engineers and information technology professionals, in both pay and promotions. The panelists peppered her with questions about how Microsoft evaluated its employees, and Judge Johnnie Rawlinson of the U.S. Court of Appeals for the Ninth Circuit repeatedly asked her to identify the policy at issue.