No, definitely not. In a strict sense, because it is not a federally scheduled drug and I didn't make any agreement with my employer not to use it on the clock.
The same argument applies to alcohol, but I've noticed that cultural expectations around drinking are a lot different. A "business lunch" with a beer is no big deal in many (most?) industries. But I've never been at a business lunch where everyone passed around a joint!
Is it your view that cannabis is a federally scheduled drug for ethical reasons? Or is your view that it's always ethical to follow laws as written? I guess what I'm getting at is that to me there doesn't seem to be any good ethical reason for cannabis to be a federally scheduled drug in the first place. In fact, given the devastation the war on drugs has caused, it's my opinion that it's unethical for cannabis to be a federally scheduled drug.