In regards to tribal casinos located on Native American reservations, slot machines played against the house and operating independently from a centralized computer system are classified as "Class III" gaming by the Indian Gaming Regulatory Act (IGRA), and sometimes promoted as "Vegas-style" slot machines. In order to offer Class III gaming, tribes must enter into a compact (agreement) with the state that is approved by the Department of the Interior, which may contain restrictions on the types and quantity of such games. As a workaround, some casinos may operate slot machines as "Class II" games—a category that includes games where players play exclusively against at least one other opponent and not the house, such as bingo or any related games (such as pull-tabs). In these cases, the reels are an entertainment display with a pre-determined outcome based on a centralized game played against other players. Under the IGRA, Class II games are regulated by individual tribes and the National Indian Gaming Commission, and do not require any additional approval if the state already permits tribal gaming.