and uses the same rules, I'm wondering whether they might deny intervention anyhow. In fact, regardless of the fact that they have original and exclusive jurisdiction, it looks like they can decline to hear it at all:
"Cases of Which the Court Has Declined Jurisdiction.—In other cases, however, the Court, centering its attention upon the elements of a case or controversy, has declined jurisdiction. In Alabama v. Arizona, where Alabama sought to enjoin nineteen states from regulating or prohibiting the sale of convict-made goods, the Court went far beyond holding that it had no jurisdiction, and indicated that jurisdiction of suits between states will be exercised only when absolutely necessary, that the equity requirements in a suit between states are more exacting than in a suit between private persons, that the threatened injury to a plaintiff state must be of great magnitude and imminent, and that the burden on the plaintiff state to establish all the elements of a case is greater than the burden generally required by a petitioner seeking an injunction in cases between private parties.
Pursuing a similar line of reasoning, the Court declined to take jurisdiction of a suit brought by Massachusetts against Missouri and certain of its citizens to prevent Missouri from levying inheritance taxes upon intangibles held in trust in Missouri by resident trustees. In holding that the complaint presented no justiciable controversy, the Court declared that to constitute such a controversy, the complainant state must show that it “has suffered a wrong through the action of the other State, furnishing ground for judicial redress, or is asserting a right against the other State which is susceptible of judicial enforcement according to . . . the common law or equity systems of jurisprudence.” The fact that the trust property was sufficient to satisfy the claims of both states and that recovery by either would not impair any rights of the other distinguished the case from Texas v. Florida, where the contrary situation obtained. Furthermore, the Missouri statute providing for reciprocal privileges in levying inheritance taxes did not confer upon Massachusetts any contractual right. The Court then proceeded to reiterate its earlier rule that a state may not invoke the original jurisdiction of the Supreme Court for the benefit of its residents or to enforce the individual rights of its citizens. Moreover, Massachusetts could not invoke the original jurisdiction of the Court by the expedient of making citizens of Missouri parties to a suit not otherwise maintainable. Accordingly, Massachusetts was held not to be without an adequate remedy in Missouri’s courts or in a federal district court in Missouri.
https://law.justia.com/constitution/us/article-3/29-suits-between-two-or-more-states.html
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