When one U.S. state wants to sue another, the case goes straight to the Supreme Court of the United States. That is the only courthouse in the country where states can sue each other, because federal law gives the Justices “original and exclusive jurisdiction” over disputes between states. The suing state files a formal request for permission, the Court decides whether to accept the case, and if it does, a Special Master usually runs the fact-finding before the Justices issue a binding decree.
Why the Supreme Court Is the Only Forum
Article III, Section 2 of the Constitution grants the Supreme Court original jurisdiction over cases “in which a State shall be Party.”1Legal Information Institute. U.S. Constitution Article III Congress then narrowed the forum further through 28 U.S.C. ยง 1251(a), which makes the Court’s jurisdiction over controversies between two or more states not just original but exclusive.2Office of the Law Revision Counsel. 28 USC 1251 – Original Jurisdiction For some other original-jurisdiction categories, like suits involving ambassadors or a state suing citizens of another state, Congress has allowed lower federal courts to hear the case as well. State versus state is different. No other court in the country can take it.
The reasoning is straightforward. States are sovereign within the federal system, and no state’s own courts could credibly claim neutrality over a dispute with a rival state. The Supreme Court sits above all of them.
What States Actually Sue Each Other Over
Interstate lawsuits cluster around a handful of recurring issues, almost all involving something that physically or legally crosses a border.
- Boundary disputes. These were the earliest and most common category. At the Constitutional Convention in 1787, serious border disputes involved ten of the original states, and boundary fights dominated the Court’s interstate docket for its first sixty years.3Legal Information Institute. U.S. Constitution Annotated – Historical Background on Controversies Between Two or More States
- Water rights. Fights over shared rivers and aquifers now dominate. The Court heard its first major water case in 1901, when Missouri sued Illinois over sewage discharged into the Mississippi River, and water disputes remain the single most active category today.4Congress.gov. Constitution Annotated – Modern Suits Between States
- Environmental harm. Pollution that originates in one state but damages another has generated its own line of cases. Ohio once tried to sue a chemical company for dumping mercury into streams feeding Lake Erie; the Court acknowledged it had jurisdiction but declined the case, finding the scientific complexity better suited to a lower federal court.4Congress.gov. Constitution Annotated – Modern Suits Between States
- Taxation and commerce. States sometimes clash when businesses operate across state lines and two states claim the right to tax the same income or transactions.
Policy disputes with national implications have shown up more recently. In 2024, Alabama and eighteen other states sought to sue California and four other states over energy-related tort lawsuits they argued were an attempt to dictate interstate energy policy. The Court denied them permission to proceed.5Supreme Court of the United States. Alabama v. California, No. 158, Orig.
How a State Files the Lawsuit
A state can’t simply walk in and file. Under Supreme Court Rule 17, the complaining state files a “motion for leave to file” along with its initial complaint, often called a bill of complaint.6Legal Information Institute. Rule 17 – Procedure in an Original Action The complaint identifies the parties, describes the dispute, and states what relief the suing state wants.
Both documents must be served on the Governor and the Attorney General of the defendant state. Service on one is not enough. The defendant state then has 60 days to file a brief opposing the motion; if nothing is filed, the Court can proceed anyway. After reviewing both sides, the Justices decide whether to grant or deny the motion, set it for oral argument, or request additional filings.6Legal Information Institute. Rule 17 – Procedure in an Original Action
The Court Can Refuse the Case
Permission is far from automatic. The Justices treat their original jurisdiction as a serious but discretionary responsibility, and they regularly deny leave to file. The Alabama v. California denial in 2024 is one example: nineteen states asked the Court to intervene in an interstate energy policy dispute, and the Court simply denied the motion.5Supreme Court of the United States. Alabama v. California, No. 158, Orig. The Ohio mercury case is another: jurisdiction existed, but the Court sent the dispute to a lower court because the scientific issues were better handled through a trial-level proceeding.4Congress.gov. Constitution Annotated – Modern Suits Between States Exclusive jurisdiction does not mean mandatory jurisdiction.
What Happens After the Court Accepts the Case
If the motion is granted, the Court almost always appoints a Special Master to manage the proceedings. The Supreme Court doesn’t hold trials. It doesn’t take live testimony or sift through boxes of documents. The Special Master does, functioning as a hybrid trial judge and investigator and playing a particularly important role in boundary and water cases where geographic and historical evidence requires intensive fact-finding.7Legal Information Institute. Special Master
The Special Master oversees discovery, holds hearings, and eventually prepares a report with recommended findings and conclusions. The parties can file exceptions arguing the Master got something wrong. The full Court then reviews the report and the exceptions, and it may adopt, modify, or reject the recommendations. The Justices are not bound by the Master’s conclusions, though they often give substantial weight to findings based on evidence the Master saw firsthand.
Expect the process to be slow. Many interstate cases take years, and some take decades. The Kansas v. Colorado fight over the Arkansas River is the extreme example: Kansas first invoked the Court’s original jurisdiction in 1901, and related proceedings were still producing Supreme Court opinions a century later in 2001.8Library of Congress. U.S. Reports: Kansas v. Colorado, 533 U.S. 1 (2001) Part of the pace is structural; original jurisdiction cases compete with hundreds of certiorari petitions every year, and the Special Master process itself takes time.
How These Cases End
Interstate disputes resolve one of two ways. The Court issues a decree, or the states negotiate a settlement.
A Supreme Court decree in an original jurisdiction case carries the same binding force as any other Supreme Court judgment, and states are legally obligated to comply. In water cases, decrees often specify how many acre-feet each state gets or impose monitoring requirements that last indefinitely. The Court retains jurisdiction and can be asked to step back in if one side violates the terms, which is what happened when Kansas filed a new complaint in 1986 alleging Colorado had violated a 1949 interstate compact; that follow-on dispute itself dragged on for at least fifteen more years.8Library of Congress. U.S. Reports: Kansas v. Colorado, 533 U.S. 1 (2001)
Settlements are the other path. States can negotiate at any stage of the proceedings, often with the Special Master’s involvement. A proposed consent decree between Texas and New Mexico, for instance, would have resolved ten years of litigation over whether New Mexico had violated the Rio Grande Compact.9The National Judicial College. Texas v. New Mexico: SCOTUS, Interstate Water Compacts and Federalism Settlements in these cases still require Supreme Court approval before they become enforceable.
Interstate Compacts as an Alternative to Suing
Litigation at the Supreme Court is expensive, slow, and uncertain, and states often reach for a different tool. The Constitution’s Compact Clause, in Article I, Section 10, allows states to enter agreements with each other, though agreements that could shift the balance of power between the states and the federal government require congressional consent.10Congress.gov. Article 1 Section 10 Clause 3 If a compact covers something the states could accomplish on their own without affecting federal interests, congressional approval isn’t necessary.11Interstate Commission for Adult Offender Supervision. Bench Book – When Consent is Required
Compacts are state-crafted and state-governed, which preserves sovereignty in a way a court-imposed decree does not. Each member state enacts the same statutory language, creating uniform standards while leaving room for local implementation. Hundreds of compacts are currently in force, covering water allocation, criminal justice, professional licensing, environmental protection, and more. The Kansas-Colorado history is a useful illustration of both the promise and the limits of this path: the compact route worked as designed for nearly forty years before litigation resumed. For a state weighing a lawsuit, a compact is often the faster and more collaborative option, but it only works if the other side is willing to negotiate.