In the Supreme Court case Wal-Mart Stores Inc v Dukes, decided in 2011, the justices ruled against allowing what would have been the largest class action lawsuit in U.S. history. The case was brought by around 1.5 million women who worked at Walmart and alleged that they faced gender discrimination in pay and promotions. The key issue in the case was whether these women could be treated as a single class for the purpose of a class action lawsuit. The Court ultimately said no, deciding that the group lacked what’s known as “commonality,” a legal requirement that all members of a class share common questions of law or fact.

The plaintiffs argued that Walmart had a corporate culture that permitted discrimination to flourish, and that the company’s policy of giving local managers discretion over hiring and promotion led to unfair treatment of women throughout the organization. They claimed that even though individual decisions were made by different managers, there was still a general pattern of discrimination that could be linked back to Walmart’s broader corporate policies. They used statistical data and expert testimony to show patterns of pay disparity and promotion gaps between men and women.

However, the Supreme Court disagreed. Justice Antonin Scalia, writing for the majority, said that because each employment decision was made at the discretion of individual managers, and there was no clear company-wide policy requiring or encouraging discrimination, the case did not meet the standard for class certification. In other words, just because many women may have experienced discrimination, that didn’t mean they all experienced the same kind of discrimination in the same way or for the same reason. That lack of a shared, central issue meant they could not proceed as a single class under the law.

The ruling had major implications for class action lawsuits going forward. It made it much harder for large groups of employees to bring discrimination cases against big corporations unless they could point to a specific, company-wide policy or practice that harmed everyone in the same way. It also highlighted how difficult it is to hold companies accountable for systemic discrimination when the discrimination is carried out through decentralized decision-making. In the end, the Court’s decision in Wal-Mart v Dukes emphasized that without a clear, unifying legal or factual thread linking all the claims, a class action cannot move forward.