What's interesting is how much of a grey area that the due process question is. Non-citizens may or may not actually legally merit due process, and to whatever degree they might, they only merit it while "within" the "jurisdiction" of the US. And as far as I can tell, that 'grey area' of how the 14th amendment is read, plus the alien enemies act, is probably legally enough to justify this - and we also have all kinds of exceptions for dealing with "terrorists" (thanks, Obama).
Lets also not forget how much legal precedent Guantanamo provides when dealing with non-citizen (or even US Citizen!) "terrorists".
I don't think you've been specific about any other laws - just a couple of guesses about 'probably violating' things.