You should fire them all for drinking and smoking cigarettes, too.
Nick, I agree what they did was freakin stupid and there should be ramifications.
Now, on a seperate note, as far as just being high on the job, if you can't tell who is, why bother? Think about it. I've worked in many, many places in many different states doing many different things. Half the world is stoned and you'd never know it. I'm no longer suprised by who I find smokes. Now, that statement wouldn't mean shit if I worked at McD's or similar, but I'm talking mulitple labs including the genetics lab I worked for; doctors there, etc. As far as I'm concerned, it's as normal as knowing someone who drinks. Well, the difference between those two is at least if I know you're high, you're less likely to crash, be depressed, or violent. lol