Tribal sovereignty and federal supremacy. In U.S. law, “Indian law” refers to the body of federal statutes, treaties, and court decisions governing Native American tribes. Tribes are treated as “domestic dependent nations” with inherent self‑government over their members and lands. The U.S. Constitution (Art. I, §8) and federal treaties give Congress plenary power over Indian affairs, and the Supremacy Clause makes federal Indian law the “supreme Law of the Land”. The Supreme Court has long held that state laws generally do not apply on reservations unless Congress clearly permits them. For example, in McClanahan v. Arizona (1973) the Court struck down an Arizona income tax on a Navajo earning all income on the reservation, explaining that “state laws generally are not applicable to tribal Indians on an Indian reservation except where Congress has expressly provided”. In other words, absent an explicit federal authorization, states lack jurisdiction on tribal lands, and any conflicting state law is presumed preempted.
Federal vs. state jurisdiction on reservations. Federal law and tribal law typically govern activities in Indian country, while state authority is limited. Congress can authorize states to exercise jurisdiction – for example, Public Law 83‑280 (1953) gave certain states broad authority over crimes (and limited civil matters) on reservations. As one BIA guide notes, PL 280 required Alaska, California, Minnesota, Nebraska, Oregon, and Wisconsin to assume jurisdiction (plus other states elected in later years). But even PL 280 states were expressly prohibited from regulating tribal governments or imposing taxes on tribes. Outside PL 280, states have no inherent authority. On the criminal side, if an event occurs on reservation land and an Indian is involved, federal law usually controls. For example, under the Major Crimes Act (18 U.S.C. § 1153), certain serious crimes committed by Native Americans in “Indian country” fall exclusively under federal jurisdiction. In McGirt v. Oklahoma (2020), the Supreme Court applied that rule to hold that Oklahoma had no jurisdiction over enumerated crimes by a Creek citizen on tribal land. (That led to Oklahoma v. Castro‑Huerta (2022), which later held that states do have concurrent jurisdiction for non‑Indians who commit crimes against Indians on reservations.) On the civil side, courts ask whether a state law conflicts with federal or tribal interests. As the Bracker case illustrates, when a state attempts to tax or regulate reservation activity, courts weigh tribal/federal interests versus the state’s. In White Mountain Apache Tribe v. Bracker (1980), Arizona tried to impose fuel and carrier taxes on non‑Indians logging tribal timber on the Fort Apache Reservation. The Supreme Court held those taxes preempted by federal law, noting that federal forestry regulations and tribal self‑government were so pervasive that state intrusion “would undermine” federal policy. In sum, unless Congress has consented (or treaties permit state action), states generally cannot enforce their laws on reservation lands, and conflicting state statutes are preempted by federal authority.
Preemption principles. The Supremacy Clause ensures that valid federal Indian law overrides state law. A legal encyclopedia notes that “federal law takes precedence over any conflicting state law”. However, Indian law applies a special presumption: state law is not assumed to cover tribal lands. One scholar explains that “state jurisdiction in Indian Country is presumed lacking” unless Congress clearly says otherwise. Put simply, absent a treaty or statute authorizing a state law on a reservation, federal and tribal law control. For instance, the Court has repeatedly held that even innocent state interests (like raising revenue) cannot overcome federal policy on tribal lands: in Bracker (cited above) and earlier cases like Warren Trading Post v. Arizona Tax Comm’n (1965), the Court invalidated state taxes on reservation business despite no direct conflict in the statute. Tribal sovereignty and the federal trust responsibility are given special weight in these preemption analyses.
Examples of Preemption in Indian Country
- Criminal jurisdiction: If an enrolled tribe member commits a major crime in “Indian Country,” federal authorities have exclusive jurisdiction under 18 U.S.C. § 1153. For example, McGirt v. Oklahoma (2020) held that multiple crimes by a Creek citizen on his reservation fell under federal Major Crimes law. By contrast, a state court may prosecute non‑Indians who commit crimes on a reservation only if Congress permits – a point highlighted in Castro‑Huerta (2022), which declared that Oklahoma (and by implication other states) has concurrent jurisdiction over crimes by non‑Indians against Indians in Indian country.
- Taxation: States cannot tax tribal members, tribal property, or reservation activities without explicit congressional authorization. In McClanahan v. Arizona (1973) the Supreme Court struck down Arizona’s attempt to tax a Navajo’s reservation income, reaffirming that tribal lands and Indians “are not subject to State taxation” absent express congressional consent. Similarly, revenues of tribal governments and enterprises on the reservation are generally exempt from state tax.
- Tribal gaming: The federal Indian Gaming Regulatory Act (1988) and Supreme Court precedent make tribes the default regulators of gaming on their lands. In California v. Cabazon Band (1987), California’s ban on reservation bingo and poker was held preempted because Congress had not authorized state regulation, and California itself permitted such gaming off-reservation. The Court observed that tribal bingo was the tribe’s only source of revenue and that federal and tribal interests in self‑government outweighed the state’s regulatory interest. Thus a tribe may operate casino games allowed by any state law, and states cannot outright prohibit on-reservation gaming unless Congress says so (IGRA then provides a framework of required state‑tribal compacts).
- Public Law 280 states: Some states voluntarily took jurisdiction over crimes on reservations. Under PL 280, California, Minnesota, Nebraska, Oregon, Wisconsin (and Alaska) are required to prosecute criminal (and certain civil) cases on reservations. But even these states may not regulate core tribal functions. The BIA notes that PL 280 “did not grant states regulatory power over tribes or lands held in trust; federally guaranteed tribal hunting, trapping, and fishing rights; basic tribal governmental functions; nor the power to impose state taxes”. Thus even in PL 280 states, tribal members retain protections (e.g. exclusive tribal jurisdiction over domestic relations, enrollment, etc.), and state laws on environment, land use, or gambling generally do not apply absent further Congressional action.
- Other civil matters: As a rule, state civil regulations (environmental permits, zoning, health and safety rules, etc.) do not apply on reservations if they conflict with federal or tribal regimes. For example, many tribes administer their own land‑use and environmental codes; a state law that interfered with those would likely be preempted by the federal policy of promoting tribal self-determination. Conversely, if a non-Indian lives or acts off-reservation, state law normally applies.
Applying the rules in practice. In the real world, the applicable law depends on context: where did the activity occur (on or off reservation)? Who is involved (tribal member, tribal entity, non-Indian)? And what did Congress say? A practical approach is: (1) Check federal law or treaty: If a federal statute (like the Major Crimes Act, Indian Commerce statutes, or IGRA) or treaty covers the situation, follow it. (2) Check tribal law: If the event is on tribal land between tribal members, tribal law (or courts) may govern, subject to federal limitations (e.g. sentencing limits under the Indian Civil Rights Act). (3) Check state authorization: Ask whether Congress has explicitly allowed the state to step in (e.g. under PL 280 or a specific statute). If not, the state usually has no authority. (4) Supremacy/Preemption: If a state law is inconsistent with federal or tribal law, it is preempted – for example, a state environmental regulation cannot be enforced on reservation lands if federal law occupies the field. In short, tribal lands are generally governed by federal or tribal law, and conflicting state laws are displaced unless Congress says otherwise.
Sources: U.S. Supreme Court opinions and federal statutes (e.g. Major Crimes Act, Public Law 280), legal treatises and articles, and official analyses (e.g. BIA FAQs) provide authoritative guidance. These sources consistently emphasize that tribal sovereignty and federal authority limit the reach of state law on reservations. Each concrete case requires examining treaties, statutes, and case law to see which level of law governs.