The US Department of Interior will decide early this year if it has legal authority to grant a reservation to the Mashpee Wampanoag, an essential requirement before the tribe can open a casino and one of the major questions hanging over the Mashpee’s plans for a Taunton gambling resort.

That legal determination may be months away, and finalizing a reservation would take longer and could result in a court challenge, but the tribe argues that it is making progress and the state should not permit a commercial casino in Southeastern Massachusetts.