BILLINGS, Mont. (AP) — Negotiations are due to resume Friday in a legal dispute between Montana regulators and a Navajo Nation-owned company that prompted the closure of one of the largest coal mines in the U.S.

State officials said they were optimistic on reaching a deal with the Navajo Transitional Energy Company.

The company took over the 275-worker Spring Creek Mine near the Montana-Wyoming border this week after acquiring it in a bankruptcy sale.

The company shut down the mine Thursday when state officials said they wouldn't approve operations unless the company waives its immunity as a sovereign tribal entity.

Waiving immunity would allow the company to be sued over future environmental violations or mine reclamation costs.

Company representatives say they won't agree to a full waiver of their treaty rights.