Women engineers who claim Microsoft Corp. discriminates against them for pay and promotions faced tough questions from a federal appeals court weighing whether their ground-breaking lawsuit should become a class action.

During arguments Monday in Portland, Oregon, the three-judge panel of the U.S. Court of Appeals challenged a lawyer representing three women suing the tech giant to explain how Microsoft’s policies favor men when managers dole out pay raises.

The panel is reviewing a Seattle judge’s June 2018 ruling that the women didn’t show enough of a common thread in their workplace experience to prove that a uniform Microsoft corporate policy or action adversely affected them. The standard was set in a 2011 decision by the U.S. Supreme Court in a gender-bias case against Walmart Inc.

U.S. Circuit Judge Johnnie Rawlinson said at the hearing that the Walmart case “tells us there has be policy in place” that applies to every decision across the board with respect to pay.

“That’s where I’m having a disconnect,” Rawlinson said. After the judges questioned attorneys on both sides, Rawlinson said: “Very little in this case is clear to me.”

The lawsuit against Microsoft is the first in a series of gender-pay-disparity cases against big technology companies to reach an appeals court over the question of class-action status. The three plaintiffs want to represent about 8,630 peers who have worked for the company since 2012. Pursuing the case on behalf a large group would give the women much stronger leverage in settlement negotiations before a trial.

Women employees at Twitter Inc. lost their bid for class-action status in July 2018 in San Francisco state court. Similar cases against Oracle Inc. and Google are pending.