The Navajo Tax Commission has a jurisdiction that includes areas of three states, Arizona, New Mexico and Utah. There are many U.S. District Court and Appellate cases, which define jurisdictional boundaries for tribal taxing authorities. The jurisdiction of the tribal taxing authorities exists only within tribal boundaries.
Non-tribal persons and entities may be subject to a particular tribal tax code if they are doing business on tribal lands. The tribes retain the authority "to tax the activities or property of non-Indians taking place or situated on Indian lands, in cases where the tribe has a significant interest in the subject matter." (Confederated Tribes of Colville Indian Reservation, 447 U.S. at 153)
Tribal tax acts have to be approved by the Secretary of the Interior. When tribal taxing authorities are challenged, the outcome is usually decided in the United States Federal Court system.