The mayors of numerous Sanctuary Cities in the United States - those which shelter or allow undocumented immigrants - have promised to take the President to court. They have stated that his recent executive order asking them to deport local immigrants is unconstitutional. If enforced, the order would cut funding from any city that failed to abide by his directive.
While there are many social, political, and economical reasons to argue against the order, what part of the Constitution are these sources referring to?
What specifically has been or can be argued, using the Constitution as a base, against this order?