While California's medical marijuana law might help an individual avoid criminal prosecution, it doesn't protect a person's job, the state's Supreme Court ruled Thursday.

The 5-2 decision clears up uncertainty about employers who fire employees for using legally-prescribed marijuana.

The ruling came as a surprise to Ventura labor lawyer Tony Strauss, who said he will need to change the advice he's been giving employers.

He has been erring on the side of caution, advising employers to let it slide if they think their employees are using medical marijuana. Strauss said he believed employees would be protected by the Americans with Disabilities Act.

"This certainly has been an issue," he said. "I've always taken the conservative approach because California is liberal in its interpretation of disabilities, and I thought this was something that would have been covered."

The question before the court was whether voters had intended to change employment law with the enactment of the Compassionate Use Act of 1996, added when voters approved Proposition 215.

The court did not find anything in the history of the act to indicate voters intended to amend the state's employment laws.

Justice Kathryn Werdegar wrote: "For a court to construe an initiative statute to have substantial unintended consequences strengthens neither the initiative power nor the democratic process; the initiative power is strongest when courts give effect to the voters' formally expressed intent, without speculating about how they might have felt concerning subjects on which they were not asked to vote."

The ruling implies that if voters want to change employment law, they can do so via another measure, said Karen Gabler, an employment law attorney and partner in Nordman Cormany Hair & Compton LLP in Oxnard.

"This is a great example of the checks and balances that our government is founded on," she said. "The courts don't make legislation, they apply legislation.

"So I thought the court was very good about fulfilling its role and not overstepping its bounds in the context of our governmental system."

The ruling stemmed from a case involving a Sacramento telecommunications company that fired Gary Ross for flunking a company-ordered drug test. He had his physician's permission to legally use marijuana to treat a back injury sustained while serving in the Air Force.

Ross took a drug test and started his job at the company, RagingWire Telecommunications Inc. A few days after he started, the company got the results back and he was fired.

As an aside, Gabler said employers would be wise not to do what RagingWire did. "If you are going to do a pre-employment drug test," she said, "don't let the person start working until you get the results."

Nonetheless, RagingWire successfully argued it fired Ross because all marijuana use is illegal under federal law, which does not recognize the medical marijuana laws in California and 11 other states.

With a 2005 U.S. Supreme Court decision declaring that state medicinal marijuana laws don't protect users from prosecution, the Drug Enforcement Agency and other federal agencies have been actively shutting down major medical marijuana dispensaries throughout California over the last two years and charging their operators with serious felony distributions charges.

RagingWire said it fired Ross because it feared it could be the target of a federal raid, among other reasons.

The Santa Clara Valley Transportation Authority and the Western Electrical Contractors Association Inc. had joined the case, arguing that companies could lose federal contracts and grants if they allowed employees to smoke pot.

The conservative nonprofit Pacific Legal Foundation said in a friend-of-the-court filing that employers also could be liable for damage done by workers who are high.

Ross' attorney had argued that medical marijuana users should receive the same workplace protection from discipline that employees with valid painkiller prescriptions do.

A dissenting opinion, written by Justice Joyce Kennard and joined by Justice Carlos Moreno, attacked the majority's ruling as "conspicuously lacking in compassion." Kennard said the ruling "disrespects" the California medical marijuana law, and employers should be barred from firing workers who use medical marijuana as long as they continue to perform their jobs adequately.

"The majority gives employers permission to fire any employee who uses marijuana on a doctor's recommendation, without requiring the employer to show that this medical use will in any way impair the employer's business interests," wrote Kennard.

— The Associated Press contributed to this report.