[Guest post by Chloe Schama:]

Last week, the Supreme Court heard oral arguments for a class-action case that NPR called “the largest sex discrimination lawsuit in U.S. history.” The description is actually a bit misleading: From a legal standpoint, the issue in  Dukes v. Wal-Mart is standing: whether or not hundreds of thousands of women—upon whose behalf former Wal-Mart employee Betty Dukes had filed the case—could band together and sue for damages. Or, as Richard Thompson Ford put it in Slate, “[W]hat’s at stake in Dukes v. Wal-Mart is whether class-action lawsuits will continue to be a way to address pervasive discrimination.”

But gender discrimination is still the core substantive issue in the case. That became clear during oral arguments, when Wal-Mart’s lawyer, Theodore Boutros, denied claims that pervasive discrimination exist in Wal-Mart’s hiring and employment practices. As proof, he pointed to the company’s explicitly anti-discrimination policies. Justice Ruth Bader Ginsburg didn’t appear persuaded. When “the company gets reports month after month showing that women are disproportionately passed over for promotion,” she probed, “and there is a pay gap between men and women doing the same job. … Isn’t there some responsibility on the company to say, is gender discrimination at work, and if it is, isn't there an obligation to stop it?” Boutros deflected the questions by calling the plaintiff’s statistical analysis into question, but he did not deny the point.

Ginsburg, a longtime advocate for women’s rights in court, was on to something. The pay disparity between men and women remains a persistent, and troubling, reality in the U.S. I’ve written about these disparities before—arguing that, even when you control for legitimate factors that affect the inequality between the wages that men and women take home, there is still, much more often than not, an inexplicable gulf. According to the plaintiffs in this case, the average hourly wage differential between male and female Wal-Mart employees could reach as high as $1.17, with this most severe disparity affecting the employees who had worked for Wal-Mart the longest.

During the oral argument presented by the plaintiffs’ lawyer, Joseph Sellers, Chief Justice John Roberts asked if it was “true that Wal-Mart’s pay disparity across the company was less than the national average.” The implication seemed to be that, if Wal-Mart’s disparity was lower, accusations of discrimination had less merit. But the existence of a larger discrimination should not excuse incidents of lesser injustice.