WASHINGTON (CNN) — Workers who are legally prescribed marijuana to treat illness can still be fired from their jobs, following a ruling Thursday from the California Supreme Court.

The 5-2 decision upheld the job termination of Gary Ross, who flunked a company drug test shortly after being hired at a telecommunications firm.

A state referendum that allows people to use medical marijuana with a physician’s recommendation are immune from some state criminal drug possession charges. But the state high court said such legal protection only goes so far.