[bluejekyll]

This is handled through most jobs requiring that people show up sober to the workplace. The same laws/rules would apply to marijuana. You can't operate heavy machinery while drunk or high, though caffeine and tobacco generally aren't regarded in the same way.

It's foolish to think people will just throw caution to the wind and get high before doing their job.

[random_upvoter]

If your employee is a habitual pot smoker there is still the risk that one day he turns up high for work. Why would you take that risk if you can hire somebody who does not smoke at all?

Other than that, consumption of cannabis is correlated with a bunch of stuff that an employer may want to avoid (for instance increased impulsivity [1])

Given the fact that employers routinely choose to not hire somebody because of even the slightest misgivings, not wanting to employ a pot smoker can hardly be called irrational.

[1] http://www.ncbi.nlm.nih.gov/pubmed/25595054

[xyzzyz]

Why would you take that risk if you can hire somebody who does not smoke at all?

Indeed, that's why I hire only teetotalers. After all, if they like to have a drink now and then, there's still a risk that one day they turn up drunk for work.

[ascagnel_]

You would think this, especially for people operating heavy manufacturing equipment, yet a quick search lists page after page of results where auto workers in assembly plants were busted, fired, and reinstated after being caught drinking and smoking before or on the job.

The first link I got from my search: http://www.torquenews.com/106/chrysler-ordered-rehire-worker...