The Citizen Band Potawatomi Indian Tribe of Oklahoma (the tribe) (defendants) ran a convenience store on their reservation. The tribe sold cigarettes at the store without collecting Oklahoma’s state cigarette tax. The Oklahoma Tax Commission (Oklahoma) (plaintiff) served a demand on the tribe for $2.7 million in back taxes. The tribe filed suit in federal district court for the Western District of Oklahoma seeking to enjoin the assessment. Oklahoma counterclaimed to enforce the $2.7 million claim and to enjoin the tribe from continuing to sell cigarettes without collecting and remitting the state sales tax. The tribe moved to dismiss the counterclaim on the grounds of sovereign immunity.