Can I be fired if I test positive for marijuana, even though weed was just legalized? What you need to know. Updated Feb 25, 2021; The short answer: for now, maybe. Under the legalization law, companies cannot fire employees unless they can prove they were high while at work using both a physical test for THC, the active ingredient in marijuana, and testimony from an expert witness. But the state Cannabis Regulatory Commission must still adopt rules and regulations to set this in stone and develop a program to train such witnesses, who will likely be people employed by the company in question. Developing those protocols could take six months.