Companies can fire employees who use marijuana for medical reasons even if California law allows such use because federal law prohibits it, says a recent ruling by the state’s Supreme Court.

“Under California law, an employer may require pre-employment drug tests and take illegal drug use into consideration in making employment decisions,” Justice Kathryn Werdegar wrote.

The court’s 5-2 decision is another blow to advocates for marijuana use for medicinal purposes, according to Reuters.

In March of last year, a federal court based in San Francisco said a California woman with an inoperable brain tumor had no fundamental right to marijuana for medical purposes.

Rulings such as this have confirmed that federal law governs when there are clashes with state law. California voters backed an initiative in 1996 allowing the smoking of marijuana for medical purposes—a use barred by federal law, Reuters said.

“No state law could completely legalize marijuana for medical purposes because the drug remains illegal under federal law,” Werdegar wrote.

In the latest case, Gary Ross said he began using marijuana in 1999 on a doctor’s recommendation because of back pain.  Ross said that after he was offered a job at a company in 2001, he took and failed a drug test and was fired. He sued the company, privately held RagingWire Telecommunications, because he said it failed to make reasonable accommodation for his disability.

The Pacific Legal Foundation, which backed the employer, said the ruling would help keep drug-impaired employees from workplaces.

Proponents of medical marijuana said they were looking for support from lawmakers in the nation’s most populous state, Reuters reported.