Luis wrote above:
[[ That makes no sense.
How can you be fired from your job for doing something completely legal on your own time?
This decision will be challenged and probably overturned. ]]
Not by the United States Supreme Court, Luis.
That court has already affirmed that employees can be disciplined or terminated for the use of certain drugs during "free time" (read on).
I was a railroad locomotive engineman for 32+ years (for Conrail, Amtrak and Metro-North).
This issue first came before the courts after the Federal Railroad Administration put into place regulations regarding railroad employee drug use and testing.
One of those regulations prohibited the use of illegal drugs not only "on duty", but OFF DUTY as well. That is to say, if one is a railroad employee in a "safety sensitive" position, that employee is prohibited from any usage of certain drugs AT ALL. And such employees are subject to random drug testing, that will enable the employer to discover such usage.
I believe it was either the Brotherhood of Locomotive Engineers, or the United Transportation Union (which represents conductors and trainmen) that filed suit over this regulation, and that went all the way to the U.S. Supreme Court.
The Supreme Court UPHELD the regulation and as such, railroad employees can be disciplined and/or dismissed for off duty drug use as well as being under the influence while on duty.
It's been this way since at least the mid 1990's.
I believe the airlines may also have such a policy as well for their own personnel in safety-sensitive positions.
One might argue that (at least in Colorado) marijuana is no longer classified as an "illegal" drug. But I doubt any case can be made there, based both on the Colorado court ruling as mentioned in the article, or the reality that marijuana -- whether legal or illegal -- can be considered a behavior-altering drug.
It's quite possible that this may get adjudicated all the way up to the U.S. Supreme Court.
But the precedent already exists (see above) to uphold the Colorado decision.