PORTLAND - Workers who smoke marijuana at home for medical purposes risk losing their jobs unless they meet a strict definition on whether they are disabled, the Oregon Supreme Court ruled Thursday in a decision that supports employers with strict drug policies.

The court also said federal law trumps state law if there is any question about marijuana in the workplace.

The case was filed by a former millwright at the Columbia Forest Products Plant in Klamath Falls.

Robert Washburn had a doctor-approved, state-issued card allowing him to use marijuana to ease leg spasms that kept him awake at night.

But Columbia has a strict “zero tolerance” drug policy that required urine tests which showed Washburn had been using marijuana.

He requested a different test to determine whether he suffered any impairment from marijuana use at home. But negotiations broke down and Columbia fired him.

A trial court sided with the company, saying that Washburn was not disabled under Oregon law because prescription medicine offered him relief from the leg spasms.

But the Oregon Court of Appeals overturned the lower court, ruling the definition of disability had to be interpreted more broadly.

The Oregon Supreme Court rejected that reasoning, siding with the trial court.

A person must suffer from a “substantial limitation” to justify medical marijuana use, and loss of sleep from leg spasms simply did not rise to that level, the court said in an opinion by Chief Justice Paul De Muniz.

In a concurring opinion, Justice Rives Kistler added that federal law pre-empts any state employment discrimination law if it requires employers to accommodate medical marijuana use.

Kistler said the federal Controlled Substances Act prohibits manufacturing, distributing or possession of marijuana - even for medical use. And he noted the U.S. Supreme Court upheld the law in a ruling on a recent California case, even though California, Oregon and nine other states have legalized medical marijuana.

The Oregon case had been cast as a showdown between workplace safety and worker medical needs.