Echazabal, who worked for an outside contractor at the plant, didn't even know he had a medical problem until he took a company health exam.
The way Echazabal sees it, the decision to keep working at the plant was his to make, even if there were health consequences. The way Chevron and a long list of employer and business groups see it, Echazabal had to go.
The Supreme Court will decide if the landmark civil rights law protecting the disabled extends to people like Echazabal. The court was hearing the case Wednesday.
The 1990 Americans With Disabilities Act says employers may not discriminate against someone who is disabled but qualified to do a job. Under some circumstances, employers must make allowances so that a disabled person can work.
"This is a perfect example of what the statute was intended to prevent," said Larry Minsky, one of Echazabal's lawyers.
Echazabal wanted the added benefits and security that came with working for Chevron itself, as opposed to a contractor. He applied and got a company job, with the condition that he had to pass a physical.
Chevron refused to hire him when tests revealed Echazabal had a chronic case of hepatitis C, a degenerative disease that can lead to cirrhosis, liver failure and death. Chevron then asked the maintenance contractor to fire or reassign Echazabal in 1996. He was fired and now drives a school bus part-time.
"Chevron decides that what's really best for Mario is if you don't work" at the plant, Minsky said.
Echazabal risked further liver damage the longer he worked around the chemicals and toxins at the El Segundo, Calif., plant, and his medical condition puts him outside the protection of the ADA, Chevron argued in court filings.
Employers must have flexibility to exclude workers who would be a danger to themselves or others on the job, Chevron argued. The Bush administration is backing the company.
"Individuals who will become sick or die from doing the job cannot work on an ongoing and reliable basis, leaving employers with disruption and the expense of hiring and training replacements," Chevron's lawyers wrote in court papers.
"Workplace injuries and deaths cause lower employee morale, reduced productivity, adverse publicity" and other problems, Chevron argued.
Knowingly hiring someone who would be harmed on the job also opens the company to lawsuits, criminal prosecution or citation for worker safety violations, the company argued.
Echazabal has no symptoms and feels fine, his lawyer said.
"He is without question qualified" for work under the ADA, Minsky said.
When Congress passed the law, its supporters said it would cover a wide range of people, from those with major physical or mental disabilities to those who might suffer discrimination as a result of even mild deformities or health problems.
The Supreme Court has repeatedly trimmed such an expansive view of the ADA, most recently with a ruling in January that makes it harder for workers to demand special treatment if they suffer partial disabilities such as carpal tunnel syndrome.
Echazabal sued in 1997, but a federal judge threw out his case. He appealed, and a divided three-judge panel of the 9th U.S. Circuit Court of Appeals ruled in 2000 that the health threat was not enough to disqualify Echazabal.
The dissenting judge wrote that such logic could mean a steelworker with vertigo gets a job working on high-rise buildings, and someone with an allergy to bee stings could be hired as a beekeeper.
Chevron appealed to the Supreme Court.
The case is Chevron v. Echazabal, 00-1406.