[Buckeye McFrog]

Article I, Section 10

Violations of that one are all over the map. States enter into compacts with other states on all kinds of things. Generally law enforcement issues or tax collection.

[jjotto]

Many such agreements have indeed been approved by Congress.

https://ballotpedia.org/Interstate_compact

...determining “whether the compact contains a political subject affecting federal interests or the interests of non-compacting sister states, in which case congressional consent is required,” is the sole basis on which the constitutionality of such agreements lies...