Yes, you may have the card, but since cannabis is still an illegal drug under federal law--federal law does not recognize the medical marijuana exception--if you use or possess it at work, you would be violating federal law (committing a crime) and could be termianted for that reason. Or if you are impaired in any way to or to any agree at work, you could be terminated for that. Or if your job involves any contracts that the city has with the federal government, or any funds provided by the federal government, even offsite possession would justify termination, since someone dealing with federal funds or federal contracts cannot violate federal law. in short, due to the fact that it is still illegallly federally, you are advised to not have or use medical marijuana in this job.