"Cardholders” — those who are legally allowed to use medical marijuana — should be handled carefully in states that specifically prohibit discrimination against them, says Danielle Urban, JD, partner with the Fisher Phillips law firm in Denver.

Simply knowing that the person is a cardholder is not enough reason to take action, she says.

“Even if you have chosen to take a zero-tolerance position, you can’t fire this person because you know he or she is a cardholder and presumably using medical marijuana,” she says. “If you’re going to take any action, I would advise against disciplining or firing the person unless you have a positive test showing the use of marijuana.”

Arizona is an example of a state that included substantial protection for card holders in its statute, notes Amanda Wingfield Goldman, JD, an attorney with the law firm of Coats Rose in New Orleans. The law includes provisions that prohibit employers from taking adverse action, such as firing cardholders based on that employee’s status as a cardholder, or even a positive drug test, unless the employee appears impaired during work hours.

The original statute left employers with no way to define impairment, so the law was revised to define impairment as evidence of negligence, carelessness, decreased coordination or dexterity, slowed or slurred speech, glassy or bloodshot eyes, and detectable odor of marijuana. The revision also gave employers protection to take adverse action in a good faith belief that the employee was impaired or using drugs during workplace hours.