The best method for determining an employer/employee’s employment rights is based upon a review of applicable state and federal laws and regulations. In lieu of this method, it is a common industry practice for an employer to comply with the state laws that are more restrictive to the employer, and most favorable to the employee as a minimum legal review. For example: Imagine you have an employee who lives in Arizona but works in California, and the employee has a medical marijuana card in which they use in private. Arizona protects employees from discrimination while holding a medical marijuana card, but in California, an employer may fire employees who test positive for marijuana, even if the use was off-duty and for a medical condition with a valid medical marijuana card. To avoid litigation in this scenario, it would be advisable to treat this employee based on Arizona laws.
It is pertinent for you, as an employer, to have a policy in place for when this occurs and to follow each states' medical marijuana laws accordingly.