The case was brought by Robert Barnett against his employer, US Airways. When Barnett injured his back while working as a cargo handler, he was transferred to a mailroom job. The job soon came open under the airline's seniority rules, and Barnett lost to more senior employees and was soon unemployed altogether. He later sued under the ADA.

The ADA prohibits an employer from discriminating against apeople with disabilities who, with "reasonable accommodation," can perform the essential functions of a job. The court ruled that requiring businesses to alter established seniority rules was not "reasonable" under the law.

Seniority systems established by union contracts were already immune from ADA challenge before the ruling. The decision now extends that immunity more broadly.