The U.S. Supreme Court has exclusive jurisdiction over lawsuits between states, and on the surface, Nebraska and Oklahoma v. Colorado, which seeks an injunction related to Colorado's state legalized marijuana industry, would seem to qualify. But, before a Complaint can be filed, a state must ask the U.S. Supreme Court for permission to file it pursuant to Supreme Court Rule 17.
Since the current lawsuit is a far cry from the usual boundary or water rights disputes between states brought in the U.S. Supreme Court's original jurisdiction, all bets are off concerning how this plays out procedurally.
It seems unlikely that the U.S. Supreme Court would refuse to take up a seemingly non-discretionary duty to take up all cases in its original jurisdiction.
But, is there any reason that permission could be denied?
In this context, the Court could treat Supreme Court Rule 17 as the functional equivalent of federal rule of civil procedure 12(b) which provides the grounds for dismissal of lawsuits prior to the filing of a formal answer to a complaint.
I think that there are several, all of which are variations on the theme of lack of subject matter jurisdiction, perhaps for lack of standing, or the closely related concept of justiciability.
1. The damages that Nebraska and Oklahoma claim to have suffered are predominantly expenses incurred not by the states themselves, but by local government law enforcement officials (and citizens) in those states. The U.S. Supreme Court could argue, therefore, that the real parties in interest are not the states, whose claims are within the U.S. Supreme Court's original jurisdiction, but the local governments of (and citizens of) those states, who are not states for purposes of 11th Amendment immunity and must sue another state in its own courts, rather than in the federal courts. Moreover, the State of Colorado would be allowed to invoke its 11th Amendment immunity for lawsuits for torts in its own courts.
2. Similarly, the U.S. Supreme Court could hold that a state does not have standing to bring claims arising out of discretionary legislative decisions made by a sister state as quasi-nuisance claims, establishing a broad, new standing rule that affects almost no other past cases and would quash similar cases in the future.
3. Alternately, and more broadly, perhaps states do not have rights to be free from tortious harm except as property owners, parties to contracts, and as expressly created by federal law. This may implicate none of these interests.
4. This standing argument would be a close cousin to the more established "political question" doctrine that holds that some issues are reserved to the political branches and may not be resolved by the federal courts. Thus, this issue might not be justiciable controversy.
5. In a similar vein, the jurisdiction of the U.S. Supreme Court consists of cases "in law and equity." But, this dispute might be deemed to be outside the scope of either the law courts, or the equity courts, at common law, and hence to be outside the subject-matter jurisdiction of the U.S. Supreme Court. England didn't have constitutional federalism at the time that British law was received in the 18th century, and certainly didn't allow one sovereign governmental entity to sue another in the fashion proposed in either the Courts of Law or the Chancery Courts. The closest equivalent jurisdiction may have been exercised by standing committees of the House of Lords, or the monarch, acting individually or through her Governor's General.
6. Finally, the U.S. Supreme Court might refuse to consider the complaint because it failed to join necessary interested parties, such as the United States government, since the supremacy of its laws and its exercise of prosecutorial discretion are at issue, or other states bordering Colorado.
Any of these procedural bars might be preferable to the Court to adjudicating this dispute on the merits for the U.S. Supreme Court as an institution, and would also resolve this urgent question much more quickly.