So, the employee will sue because there is no proof of impairment.
The link you posted said nothing about implied use at work, it was about whether there was use without a prescription.
However, if you have something similar from Colorado, I'd be interested in that, specifically in relation to recreational use.
What you aren't recognizing is that impairment can and does continue after use, thus the need for the testing in the first place. You seem to be suggesting it should be okay to use marijuana right before coming to work, so long as they don't actually use it AT work. If they are impaired they are impaired, and thus making their workplace less safe and prone to risk. Employers are risk averse.
Marijuana is an impairing substance whether or not it is legal, which is why, it will still be subject to testing when it is legal, and rightly so.
Your logic is... well, not. TCH levels can be found up to
ten days after smoking. That is what a pot test will detect.
Smoking before going to work would be the same as doing shots of vodka before going to work. Both of which would make one imparied. But that's
not what the test is doing. It's testing if you have TCH in your system,
not if you're high.
If I take a shot on Friday, and smoke a joint on Saturday, and do nothing else all weekend, hopefully you'll say I was not impaired on Monday. And a drug test on Monday would show I have no alcohol in my pee, but I do have TCH.
But you're saying that I should be fired, even though I am not impaired at work, and yet my drug test is positive.
Again, what are the business rules in Colorado for recreational use? I'd be interested to find out.