At least in the US, we're at will employment. So while we may not be able to forced to pee in a cup, we can and will be terminated if we don't comply.

Most places that have heavy machinery or manufacturing have formal drug policies with random testing. I have a relative that's an electrician and he's been randomly selected and had a coworker fail a test. Instead of firing the guy outright,they gave him an option to go to some class instead. He quit and changed careers given that choice.