WILLISTON, N.D. (AP) – Members of North Dakota's oil-rich Mandan, Hidatsa and Arikara Nation are calling for the results of an investigation into the business dealings of the tribes' chairman to be made public just days before he faces off against five challengers in a primary election.

Earlier this year, the tribes' elected body, the Tribal Business Council, hired a law firm to conduct an investigation into chairman Tex Hall's business dealings with companies operating on the Fort Berthold Indian Reservation. The investigation was led by former U.S. Attorney Stephen Hill, who presented the investigation's findings to the council in a closed session last month.

The tribes' spokeswoman, Glenda Embry, said at the time that Hall would have several weeks to respond. But the chairman's discussion of the report came late Thursday night in another closed-door meeting.

In a statement Friday, the Tribal Business Council said that the chairman's response is under review by the body and that the council will make additional comments once the review is complete. The statement did not add any details on the content of the report or whether it would be made public.

The primary is Tuesday. The top two vote-getters will face off in a general election in November.

Lane Vocu, a tribal member who was disqualified from the chairman election based on ancestry laws, said he is helping organize a protest at tribal headquarters on Monday to try to get the investigation released.

Vocu said protesters will “see if we can interrupt day-to-day activities enough for the report to be released.”

Damon Williams, the tribes' attorney who is also a candidate for chairman, said he was dismayed that the report was not released. Williams launched an investigation into Hall's business dealings earlier this year. He said his report prompted the council to hire outside investigators from law firm Dentons US LLP. In August, the firm confirmed they were investigating Hall's business dealings.

Fort Berthold Indian Reservation represents about a third of the more than 1 million barrels of oil a day currently produced by North Dakota. During the election campaign, candidates and voters have challenged that the current administration has been opaque about how the tribe spends money generated by oil boom.

Hall did not immediately phone calls from The Associated Press on Friday afternoon. Multiple requests to interview Hall made through the tribes' spokeswoman have not been granted in recent weeks.

Tex Hall | Bakken Energy Service photo