With the dismissal of a sex-discrimination lawsuit brought on behalf of 1.5 million women who have worked at Wal-Mart, the Supreme Court on Monday significantly tightened the rules for how a large group of individuals can join together to sue a company for alleged harm done to them.

The court’s decision will not just make it harder to bring big, ambitious employment class-action cases asserting discrimination based on sex, race or other factors, legal experts said. In the majority opinion, the court set higher barriers for bringing several types of nationwide class actions against a large company with many branches.

In its majority opinion, the court essentially said that if lawyers brought a nationwide class action against an employer, they would have to offer strong evidence of a nationwide practice or policy that hurt the class. In the Wal-Mart case, the court wrote that the plaintiffs had not demonstrated that Wal-Mart had any nationwide policies or practices that discriminated against women. The opinion, written by Justice Antonin Scalia, noted that Wal-Mart’s official corporate policy opposed discrimination, while the company gave the managers at its more than 3,400 stores considerable discretion over pay and promotions.

“In a company of Wal-Mart’s size and geographical scope, it is quite unbelievable that all managers would exercise their discretion in a common way without some common direction,” Justice Scalia wrote.