Well what sort of law is that? That's like saying to, I dunno... the incredible hulk "No you can't do this". I mean, what's actually stopping him aside from some arbitrary law?
And what's the nature of this magical chain attachment? I apologize if I seem rude, it's just I don't see this sort of concept a lot and now I'm mighty curious on how people may handle it.
Edit: Oh, also, what sort of stuff will we actually do? I assume the PC's will have some minor infighting on what to actually do with the devil himself until they figure out (or kill/ditch the dissenters) what they wish to do, then do that thing? E.G. bring him to hell so he can continue doing his thing, or bring him to heaven so God can pass a proper judgement, or just kill him themselves and be done with it?