As marijuana becomes legal in many states, one question remains: Can employers prohibit their employee’s from using marijuana?

In Colorado, the answer is “yes.”

On June 15, the Colorado Supreme Court unanimously held in Coats v. Dish Network that employers can discipline and terminate employees who test positive for the drug, even though recreational and medical marijuana use is allowed in the state. The reason

The reason? It’s still illegal on the federal level.

According to a Washington Post article advocates of reforming drug policy say the case highlights “the problematic gray areas that exist between state and federal law,” which often are in conflict.

The federal government still categorizes marijuana a Schedule I substance, which the Drug Enforcement Administration considers to include “the most dangerous drugs.”

In Florida, marijuana use is still prohibited. A constitutional amendment to allow medical marijuana was unsuccessful on last year’s ballot, though supporters are working on trying again in 2016. Once that happens, a similar employment question could be raised in Florida.