FLAGSTAFF, Ariz. (AP) – Members of the Hopi Tribe are going to the polls this week to vote on a revised constitution.

The draft constitution reorganizes the tribal government under four branches, and creates a presidency and vice presidency.

The current government is unicameral with most powers resting with the Tribal Council. The tribal chairman and vice chairman are part of the council.

Critics say the proposal undermines the sovereignty of 12 Hopi villages by making them part of the central government. They have sought court orders to halt Thursday's election.

Supporters say the revised constitution stabilizes the tribal government and clarifies roles within it.

Thirty percent of registered voters must cast a ballot for the election to be valid.

The tribe adopted a constitution in 1936 as part of the Indian Reorganization Act.