ASHINGTON, May 27 — In a surprising break with its march toward states' rights, the Supreme Court ruled today that states can be sued for violating their employees' federally guaranteed right to take time off for family emergencies.

The vote to reject Nevada's claim to constitutional immunity from suit under the Family and Medical Leave Act was a decisive 6 to 3. Most unexpectedly, the author of the majority opinion was Chief Justice William H. Rehnquist, under whose leadership the court has produced a series of bitterly contested 5-to-4 decisions expanding the scope of the states' immunity from suit and, correspondingly, curbing the power of Congress to make federal law fully binding.

Justice Sandra Day O'Connor joined the chief justice in abandoning their allies in these earlier decisions, leaving Justices Anthony M. Kennedy, Antonin Scalia, and Clarence Thomas in dissent today. In addition to Justice O'Connor, Justices David H. Souter, Ruth Bader Ginsburg and Stephen G. Breyer joined Chief Justice Rehnquist's majority opinion. Justice John Paul Stevens concurred separately. The decision affirmed a 2001 ruling by the United States Court of Appeals for the Ninth Circuit, in San Francisco.

The majority opinion today reviewed the recent Supreme Court rulings that immunized states from lawsuits by their employees for age discrimination and disability discrimination, explaining why the Family and Medical Leave Act required a different analysis and outcome. The family leave act was more "narrowly targeted" than the others and addressed a workplace problem that was persistent and well documented, Chief Justice Rehnquist said. [Excerpts and full text are linked at right.]

The key to the outcome of the case lay in the chief justice's conclusion about exactly what problem Congress intended to address when it passed the family leave measure 10 years ago. Endorsing the view of the act's proponents, he said the goal then was to "protect the right to be free from gender-based discrimination in the workplace" by removing "the pervasive sex-role stereotype that caring for family members is women's work."

The law sought to accomplish this, he said, by granting up to 12 weeks of unpaid leave a year to both women and men to deal with family illnesses and other emergencies. By giving men and women the same entitlement, "Congress sought to ensure that family-care leave would no longer be stigmatized as an inordinate drain on the workplace caused by female employees, and that employers could not evade leave obligations simply by hiring men," he said.

In adopting this analysis, the court rejected Nevada's argument that the law should be seen as a federal labor regulation that simply conferred a benefit of employment. The distinction was crucial. Under the court's recent precedents, Congress lacks the ability to abrogate the states' constitutional immunity from lawsuits under the general authority to regulate interstate commerce. The only way Congress can overcome state immunity is by its power under Section 5 of the 14th Amendment to "enforce, by appropriate legislation," that amendment's guarantees of equal protection and due process.

For the Family and Medical Leave Act to prevail over the immunity from suit that the 11th Amendment confers on the states, it therefore had to be accepted by the court as a remedy for discrimination. But that would not be enough. The Age Discrimination in Employment Act and the Americans With Disabilities Act also dealt with discrimination, but the court found that these were insufficient to overcome the states' immunity.

For the family leave law, the difference was that sex discrimination, when engaged in by the government, is presumed to be unconstitutional, unlike discrimination against the elderly and the disabled, which the court's precedents deem acceptable as long as the discrimination has a "rational" basis. In the majority opinions curbing the reach of the age discrimination and disabilities laws, the court rejected Congress's findings that discrimination by state employers was pervasive.

Mere rationality is not enough to justify sex discrimination, which is subject to "heightened scrutiny" under the court's equal protection doctrine. Consequently, Chief Justice Rehnquist said, "it was easier for Congress to show a pattern of state constitutional violations," and those findings were entitled to a greater degree of deference from the court.

The Family and Medical Leave Act was an appropriate remedy for the violations that Congress found in its study of the problem, Chief Justice Rehnquist said. It was "narrowly targeted at the fault line between work and family — precisely where sex-based overgeneralization has been and remains strongest." Invoking the test that the earlier cases had established, he added that this law was "congruent and proportional to the targeted violation" and was therefore a valid abrogation of the states' immunity.

The debate between the majority and the dissenters was framed as one over the quality of Congress's evidence. There was a "paucity of evidence" to support the conclusion that states were engaging in widespread sex discrimination of a sort that would be remedied by the family leave law, Justice Kennedy said in a dissenting opinion that Justices Scalia and Thomas also signed. "This is an entitlement program, not a remedial statute," he said. He added that the fact that sex discrimination receives heightened judicial scrutiny was not enough to relieve the law's defenders of the burden of showing that there was a pattern of unconstitutional conduct by the states that this law could address in an appropriately tailored fashion.

But in fact, the debate in Nevada Department of Human Resources v. Hibbs, No. 01-1368, appeared to be less over facts and figures than over what the court most needed to say at this point in the evolution of the federalism revolution that is certain to be considered one of the Rehnquist court's major legacies. Among those engaged by the issue, this case was widely seen as a potential watershed because it moved the debate about Congressional authority close to the core of traditional civil rights concerns. The Bush administration along with dozens of current and former members of Congress urged the court to uphold the full reach of the law.

"It shows that the majority was very aware of not taking this too far and provoking a public reaction against the court for undoing really important civil rights legislation," Professor Robert C. Post, a law professor at the University of California at Berkeley, who has written widely on these cases, said today.

The case began as a lawsuit by a Nevada state employee, William Hibbs, whose leave to care for his ailing wife evolved into a dispute over his rights under the family leave law. He was dismissed after failing to return to work when his supervisors told him he had exhausted his leave. The case has not yet gone to trial. The Federal District Court in Nevada found the state immune and dismissed the lawsuit. The Ninth Circuit reinstated it and the state appealed to the Supreme Court.