Sure they do, any amount in their system now and they can be fired without recourse. That fact keeps the majority from using it.
Make it legal and a company would have a hard time proving they smoked it at lunch and not on the weekend.
The same lawyer that will sue you for firing them would turn around and sue you if they hurt someone. It’s not worth the bother, fire them all and move to China.
BS. Some companies are firing because of positive tobacco tests.
Some companies will fire you if you have a beer at lunch.
Legalizing dope won’t change that you can be fired for pretty much anything.
/johnny