Although, for many years, respondent Indian Tribe has sold cigarettes at a convenience store that it owns and operates in Oklahoma on land held in trust for it by the Federal Government, it has never collected Oklahomas cigarette tax on these sales. In 1987, petitioner, the Oklahoma Tax Commission (Oklahoma or Commission), served the Tribe with an assessment letter, demanding that it pay taxes on cigarette sales occurring between 1982 and 1986. The Tribe filed suit in the District Court to enjoin the assessment, and Oklahoma counterclaimed to enforce the assessment and to enjoin the Tribe from making future sales without collecting and remitting state taxes. The court refused to dismiss the counterclaims on the Tribes motion, which was based on the assertion that the Tribe had not waived its sovereign immunity from suit. The court held on the merits that the Commission lacked authority to tax on-reservation sales to tribal members or to tax the Tribe directly, and therefore that the Tribe was immune from Oklahomas suit to collec