As far as I know the Equal Employment Opportunity Commission doesn’t recognize marijuana users as a protected class. Its up to state law to recognize marijuana users as a protected class in employment if they want to. If they don't then you can be fired for testing positive for marijuana just like you can be fired for being a nicotine user in most states or you can be fired for a whole host of behaviors both illegal and legal. The companies doing drug test will continue.
http://www.hrmorning.com/ban-hiring-smokers/