Chalk up a big win for employers and the defense bar. On Monday, in Dukes v. Wal-Mart, the Supreme Court held that the country’s largest employment class action in history—covering 1.5 million current and former female employees of Wal-Mart—could not go forward because it had been improperly certified by the lower federal courts.

The nearly decade-old lawsuit alleged that Wal-Mart discriminated against all female employees in its pay and promotion decisions according to a “policy” that was based on the discretionary decision-making of local supervisors. Plaintiffs alleged that the corporate culture at Wal-Mart was permeated with gender bias, which in turn infected the pay and promotion decisions of local managers. But a majority of the Court was troubled by the seeming contradiction of a uniform policy that was supposedly composed of the subjective decisionmaking of literally thousands of local supervisors. With this tension in mind, the Supreme Court blocked the class action because the plaintiffs had not produced enough evidence of a company-wide discriminatory pay and promotion policy.