In Wal-Mart v. Dukes, the Supreme Court ruled against a group of about 1.5 million women who wanted to file a class-action lawsuit claiming Wal-Mart discriminated against them in pay and promotions. The key issue was commonality — meaning the women had to show they all faced the same kind of discrimination in a similar way.

The Court decided there wasn’t enough common ground to group all their claims together. Since the women worked in different stores with different managers, and there wasn’t a clear, company-wide policy of discrimination, the justices said their experiences were too different to be handled as one case.

So even though many women may have felt they were treated unfairly, the Court said each case would need to be looked at individually. This ruling made it much harder for large groups of people to bring class-action lawsuits unless they can clearly prove a shared experience or pattern of harm that connects them all.