The Wal-Mart case was decided unanimously, but it was 5-4 in a very important way.

Permit me to explain what is a bit complicated. Under Federal Rule of Civil Procedure 23, which governs class action, there is a set of preliminary requirements in subsection (a) and then a list of 3 types of class actions in subsection (b). The class must meet all the requirements in (a) and then fit one of the categories in (b).  The Scalia opinion (joined by the Chief Justice and Kennedy, Thomas, and Alito) and the Ginsburg opinion (joined by Breyer, Sotomayor, and Kagan)  agree that the district court erred in putting the class into the second category in subsection (b), but only the Scalia majority also thought a preliminary requirement in 23(a) was not met. Since all class actions — in any of the (b) categories — must meet the requirements in (a), the Scalia opinion has a much more restrictive effect on class actions.

Let's focus on that disagreement. The proposed class included all current and former female employees of Wal-Mart, well over a million women. Rule 23(a) requires that all the members of the class share a common question of law or fact. Wal-Mart had a policy of decentralizing employment decisions to the store level, and the plaintiffs, attempting to satisfy 23(a), said that Wal-Mart has "a strong and uniform 'corporate culture' [that] permits bias against women to infect, perhaps subconsciously, the discretionary decisionmaking of each one of Wal-Mart’s thousands of managers — thereby making every woman at the company the victim of one common discriminatory practice."

Is this policy of decentralizing decisionmaking a common question? Scalia called it "a policy against having uniform employment practices." There have been cases in which an "undisciplined system of subjective decisionmaking" has been held to violate Title VII (the federal statutory law about employment discrimination). But in the case of Wal-Mart, once the decisionmaking was decentralized to the store level, there would be differences from store to store in how that decisionmaking would be done. Even assuming there was an undisciplined system of subjective decisionmaking in every store, each  store would might have its own undisciplined system of subjective decisionmaking. To meet the Rule 23(a) requirement of a common question, Scalia wrote, there would need to be a "specific employment practice" that was applied to all the members of the class, not simply a policy that created the conditions for thousands of stores to devise specific employment practices. 

Ginsburg thought that Wal-Mart's delegation of discretion, "uncontrolled by formal standards, has long been known to have the potential to produce disparate effects."

Managers, like all humankind, may be prey to biases of which they are unaware. The risk of discrimination is heightened when those managers are predominantly of one sex, and are steeped in a corporate culture that perpetuates gender stereotypes."...

Ginsburg tried to portray Scalia as importing a requirement that the common questions predominate over the individual questions. (That actually is a requirement in one of the subsection (b) categories.) But that's not what Scalia did. Scalia said that the decentralization move simply wasn't a question in the case and that the actual questions are specific to the store level and not to the entire class the plaintiffs attempted to define.

ADDED: After reading the case and trying to explain it as clearly as I could, I've been reading some of the press accounts, and... I can't say I'm surprised, but what politicized drivel!