A proposed law in Massachusetts would bar employers from firing workers for using marijuana legally on their own time.

While recreational marijuana use is legal for adults in the state, workers can still be fired for using the drug, even if it’s outside of work and its effects have worn off by the time they return to their jobs.

The Boston Globe reports the measure filed by Democratic state Sen. Jason Lewis would treat marijuana much like alcohol. Employees could be fired for showing up to work impaired, but employers could not police the private use of pot.

Federal contractors would be exempted as marijuana remains illegal under U.S. law.

There is currently no reliable test for marijuana impairment and drug tests can detect traces of cannabis days or weeks after use.