The Supreme Court heard oral argument Tuesday on a challenge to the certification of a class-action lawsuit on behalf of female employees against the giant retailer Wal-Mart. In the case Wal-Mart Stores v. Dukes, Wal-Mart is challenging a 9th Circuit certification of a class of all female employees, arguing it violates due process and FRCP 23(b)(2) by creating an expansive class without cohesion whose claims are dissimilar and conflict with one another.

During oral argument, justices seemed to split along gender lines, with Justices Ginsberg, Kagan, and Sotomayor questioning Wal-Mart’s counsel most closely, while Justices Scalia and Kennedy concentrated their questions on counsel representing the women employees. The suit began in 2000, when Wal-Mart employee Betty Dukes sued the company for violations of Title VII of the Civil Rights Act of 1964. Plaintiffs seek to represent a possible 1.5 million women who have worked for Wal-Mart since December 1998, arguing Wal-Mart denied women promotions and higher pay.