The 1990 Americans with Disabilities Act prohibits an employer from discriminating against a disabled person who can perform a job with "reasonable accommodation" on the part of the employer.
Writing for the majority in Monday's decision, Justice Stephen Breyer said the key word was "reasonable."
"In our view, the seniority system will prevail in the run of cases," Breyer said. "As we interpret the statute, to show that a requested accommodation conflicts with the rules of a seniority system is ordinarily to show that the accommodation is not 'reasonable.' "
However, Breyer left the door open to some cases in which "special circumstances" allowed a person's rights under the ADA to trump seniority -- for instance, if an employer is constantly changing the seniority rules.
Though they joined Breyer's majority opinion, Justices John Paul Stevens and Sandra Day O'Connor each wrote concurring opinions offering further reasoning for the judgment.
Four justices dissented -- two because they thought the majority opinion went too far and two because they thought the majority didn't go far enough.
"Indulging its penchant for eschewing clear rules that might avoid litigation," the majority's opinion produces "uncertainty," Scalia said.
"The conclusion that any seniority system can ever be overridden is merely one consequence of a mistaken interpretation of the ADA that makes all employment rules and practices ... subject to suspension when that is (in a court's view) a 'reasonable' means of enabling a disabled employee to keep his job," the justice added.
"Nothing in the ADA insulates seniority rules from the 'reasonable accommodation' requirement, in marked contrast" to the Civil Rights Act and the Age Discrimination in Employment Act.
In the case that brought Monday's decision, Robert Barnett worked for 10 years as a customer service agent for U.S. Airways and its predecessor, Pacific Southwest Airlines.
In 1990, Barnett injured his back while working as a cargo handler for U.S. Airways in San Francisco. After returning from disability leave, he used his seniority to transfer to the company's mailroom.
In 1992, Barnett's doctor and chiropractor both recommended that he avoid heavy lifting and bending, as well as prolonged standing or sitting.
When Barnett learned he was about to lose his mailroom job because two employees were exercising their seniority rights for a transfer -- bumping him back to the cargo area -- he asked his supervisor to let him stay in the mailroom as a "reasonable" accommodation under the ADA. The request was denied.
Though the Equal Employment Opportunity Commission ruled that he was not being denied "reasonable" accommodation, Barnett sued in federal court under the ADA.
A federal judge ruled for the company without hearing argument, but a U.S. appeals court reversed.
The airline then asked the Supreme Court for review, and the justices heard argument in December.
Monday's decision vacates the lower-court ruling and orders a new hearing based on the majority high court opinion.
(00-1250, U.S. Airways Inc. vs. Barnett)