This is an executive order. As such, I believe the theory is that the congress has already written the law, and that it is now up to the executive (the president) to interpret and implement what congress wrote. What we have here is the new administration's interpretation. Unless the congress comes back and corrects the administration's interpretation (or the courts declare it unacceptable per the constitution), this is immediately the law of the land. Someone with more legal knowledge than I have can correct me on this, but I believe this is where we are in the process.