Certain agreements are definitely allowed: https://en.wikipedia.org/wiki/Interstate_compact https://en.wikipedia.org/wiki/Interstate_compact Of note: "Not all

Certain agreements are definitely allowed: https://en.wikipedia.org/wiki/Interstate_compact https://en.wikipedia.org/wiki/Interstate_compact Of note: "Not all compacts between states require explicit Congressional approval – the 1893 Supreme Court decision in Virginia v. Tennessee affirmed that only those agreements which would increase the power of states at the expense of the federal government required it." I'm not claiming that this pact is formally one of these "interstate compacts", but your maximalist reading of that article forbidding "all kinds of agreements" seems to be incorrect.