The Indian Gaming Regulatory Act (IGRA), 25 U.S.C. § 2701 et seq., which regulated gaming on Indian reservations, created a national Indian gaming commission (commission) (defendant) to investigate and audit certain classes of gaming and to promulgate regulations to implement the IGRA. Class II gaming (e.g., bingo, lotto, pull-tabs) was regulated jointly by the commission and the tribes and was subject to outside audit. Class III gaming (slots, roulette, blackjack) was regulated pursuant to tribal-state compact. The Colorado River Indian Tribes (Tribe) (plaintiff) conducted class III gaming on the reservation pursuant to compact with the State of Arizona. The commission later enacted minimum internal-control standards governing class II and class III gaming and sought to audit the Tribe’s class III gaming for compliance with the new standards. The Tribe objected, claiming that the commission was not authorized under the IGRA to conduct the audit, and later sued in district court. The district court held that the commission had no authority under the IGRA to audit or regulate class III gaming. The commission appealed.