I just want to be clear that in our scenario the ONLY way anyone ever got drug tested is if they were involved in an incident in which someone got hurt. That was a Workman's Comp mandate and there was nothing we could have done to change it even if we wanted to. I had absolutely no desire to try to expose the recreational drug users through any kind of pre-employment or random testing. Our policy applied only to working hours, not the lives of employees in general. The only way I cared about what they did on their own time was if the effects of whatever they ingested lingered into the work day. That happened more than you might think.

In a non-governmental sense a workplace is a private enterprise. The employer should have the right to implement pretty much any policy regarding employees codes of conduct that they see fit (assuming they all fit within standard, non-discriminatory practices). Almost every company has some kind of dress code defining what is appropriate and what is not in their workplace. Anyone who applies to UPS knows they will have to wear ugly brown uniforms if they're hired. The applicants can decide if that's ok or if its more than their fashion sense can stand, but there is no violation of anyone's civil rights because UPS has a my way or the highway approach to uniforms. A no drug policy isn't much different as long as it is clear from the beginning. Successful applicants can decide if they would rather take the job or take the drugs. Since they are free to choose at that point no civil liberties are compromised.

The shortest route I see to a witch hunt is letting the insurance companies get involved. IMO it's virtually guaranteed if they get their way.