Yes.
Even here in WA state where pot is legal.
Would you let your factory workers use heavy machinery while on pot (or any intoxicant)?
We do random and "for cause" breath alcohol tests and drug tests in my office all the time.
Since pot was legalized we've seen a large upswing in people who come in actually high. As in they just smoked a doobie on the job.
These are industrial jobs, too.
I guess the question is whether they can be fired for being high over the weekend, rather than on the job. I've heard THC sticks around in the bloodstream for weeks after it's smoked.