In the Wal-Mart v. Dukes case, the Supreme Court said the women could not sue as a group (class-action). The Court explained that they did not have “commonality,” which means they didn’t all share the same problem that could be solved in one case.
The women said local managers were unfair, but the Court said managers made different decisions in different stores, so there wasn’t one big problem affecting everyone the same way. Without this, they couldn’t sue as one group.