I was speaking generically about "law", but you are correct that this is indeed covered specifically by the 14th amendment. I think the argument I'm trying to make is more around the definition of due process and equal protection. For example, if a person commits grand larceny by robbing a bank, and a city has that person in custody, they most certainly will turn that person over to the feds. Consequently, by definition, an illegal immigrant has committed at least one felony. I'm sure the devil is in the details around the process for handover, which is why I am lamenting the fact that the liability issue is in play because it is understandable that this puts cities in a bad spot.