Besides, it's not like muggles are a protected class. And if they were? Just keep them from applying in the first place, by building your office somewhere they can't get to. There aren't any legal restrictions on that.

My google-fu is not strong enough to find the legal doctrine, but in the US at least, you can be sued for ~implicit discrimination, i.e. if the newspaper you advertise in has a reader population that does not refelect the general population, you're discriminating against the under represented population.