In the case, Mario Echazabal was diagnosed as having a liver disease during a pre-employment physical exam by Chevron for a position at one of the company's refineries.

Chevron determined that Mr. Echazabal's liver might be further damaged by exposure to certain chemicals at the refinery, and thus denied him the job.

Mr. Echazabal sued Chevron under ADA, charging that he was the victim of discrimination based on a disability.

The U.S. District Court for the Central District of California ruled in favor of Chevron, but the 9th Circuit Court of Appeals reversed.

Chevron argued that it reasonably concluded that Mr. Echazabal would face a direct threat to his own health if he worked at the refinery.

Chevron cited an ADA provision, which says that employers may require that an employee not pose a direct threat to the health and safety of others in the workplace.

The company argued that this provision also applies to situations like this one in which the individual poses a threat to his own health.

But the 9th Circuit disagreed. On its face, the 9th Circuit said, the law only applies to others in the workplace, not to the individual himself.

Moreover, the court said, one of the purposes of ADA is to protect individuals from "overprotective rules and policies" that are one form of discrimination facing those with disabilities.

Indeed, the court said, other courts, including the U.S. Supreme Court, have generally interpreted employment discrimination statutes to prohibit "paternalistic" employment policies.

The Supreme Court is expected to rule on the case by the end of June.