The White Mountain Apache Tribe (Apache Tribe) (plaintiff) harvested timber on the reservation, using proceeds from sales to fund tribal programs. The Fort Apache Timber Company (FATCO), organized by the Apache Tribe, employed tribal members to manage the harvesting operations. Under a contract approved by the federal government, FATCO hired a non-Indian corporation, Pinetop Logging Company (Pinetop) (plaintiff), to fell and transport trees to FATCO’s sawmills. Pinetop operated solely on the reservation. Several years after timber operations began, the State of Arizona (defendant) assessed a carrier license tax and an excise fuel tax against Pinetop. Pinetop paid under protest and sued to enjoin the taxes. Pinetop argued that the state tax was preempted by federal law and interfered with tribal self-government. The Apache Tribe intervened, having agreed to reimburse Pinetop for all taxes paid to the state. The Arizona state courts upheld the Arizona tax. The United States Supreme Court granted certiorari.