Professor Dorf -- who was not involved in the case -- says the justices disagreed about whether there was a "common question."

MICHAEL DORF: "A common question, according to the court, is the sort of question which the plaintiffs can prove and thereby go a long way to winning the case."

He says most of the justices found that Wal-Mart was not being accused of one kind of discrimination or one policy, but many different acts.

MICHAEL DORF: "The key to being able to bring a class action here and the issue that divided our Supreme Court was whether all of these different claims -- by over a million people -- had enough in common to justify a single class action.”

Wal-Mart has a policy barring discrimination. But the women accused the company of unfair policies and permitting bad behavior by some store managers.

The court was divided five to four in its ruling. Yet all nine justices agreed that the case could not go forward. The women needed to meet additional legal requirements because they were seeking payment for harm they say was done. All the justices agreed these requirements had not been met.

Boston University law professor Michael Harper says the decision was widely expected. He says the class action failed because it did not target a single action or policy by Wal-Mart. But the ruling does not bar the women from bringing individual cases. They can also seek class actions at the state level.