BANGOR, Maine — The U.S. Department of Justice has asked a judge to allow it to join a lawsuit filed by the Penobscot Nation against the state over the enforcement of fishing regulations.

The Penobscot Indian Nation last August sued the Maine attorney general and the heads of the Maine Department of Inland Fisheries and Wildlife and the Maine Warden Service over who has authority over the waters of the Penobscot River surrounding the reservation.

The tribe seeks to stop Maine game wardens from policing the river and preventing tribal members from engaging in sustenance fishing.

“The nation’s jurisdiction over sustenance fishing by its members in the Penobscot River is an exercise of its inherent sovereign authority, as a matter of federal law, and it remained intact; it has never been surrendered by treaty or by an act of Congress,” the lawsuit claimed.

The lawsuit was filed after the tribe received a copy of a letter dated Aug. 8, 2012, and signed by then-Attorney General William Schneider. The letter, which was addressed to Chandler Woodcock, who was commissioner of DIF&W at the time, and Col. Joel Wilkinson of the warden service, said the tribe has the authority to regulate hunting, trapping and the taking of other wildlife on Indian Island and the islands that the tribe owns north to Medway but not on the Penobscot River.

“In recent months, the Penobscot Tribe has disagreed with the State of Maine’s long standing interpretation regarding the jurisdiction of a portion of the Penobscot River that stretches approximately 55 miles,” the head of the warden service said last year. “This circumstance has caused confusion among user groups that enjoy the many recreational opportunities that the river provides to both Penobscot tribal members and citizens and visitors to the state of Maine. The Maine Warden Service requested, for enforcement purposes, clarification and guidance through the Maine attorney general’s office.”

“Like private landowners, the Penobscot Nation may also restrict access to their lands, here islands, as it sees fit,” Schneider wrote in response to Wilkinson’s request. “However, the river itself is not part of the Penobscot Nation’s reservations, and therefore is not subject to its regulatory authority or proprietary control.

“The Penobscot River is held in trust by the state for all Maine citizens, and state law, including statutes and regulations governing hunting, are fully applicable there,” he continued. “Accordingly, members of the public engaged in hunting, fishing or other recreational activities on the water of the Penobscot River are subject to Maine law as they would be elsewhere in the state, and are not subject to any additional restrictions from the Penobscot Nation.”

In its motion to intervene, filed last week, the Justice Department said that, while intervention is “not a step the United States takes lightly,” it essentially had to join the lawsuit. This is because of its “trust obligations” to the nation’s Indian tribes and because the Maine Indian Claims Settlement Act, which was ratified by Congress, requires federal oversight. The terms of the settlement were enacted through the Maine Implementing Act.

In the filing, the department describes the case largely as a boundary dispute and says it has an obligation to ensure tribal reservation boundaries are respected.

“The United States has a two-fold interest in this litigation,” the motion says. “First, as part of its trust obligation to the Nation, the United States has a legal interest in protecting the Nation’s reservation borders and ensuring that the Nation can fully exercise its sovereign powers within those borders without improper interference from the State and others.”

The motion continues: “Second, insofar as this litigation involved questions about how the MICSA and the MIA define the Nation’s reservation boundaries, the United States has an interest in how federal statutes affecting the rights and interests of Indians are interpreted by the courts.”

Efforts Wednesday and Thursday to reach Steven Miskinis, the attorney with the Environmental and Natural Resources Division of the U.S. Department of Justice in Washington, D.C., were unsuccessful.

A coalition of towns and businesses along the Penobscot River filed a motion to intervene in the case. The coalition, including Great Northern Paper, Lincoln Paper and Tissue, Veazie Sewer District and the towns of Brewer and Lincoln, was granted intervenor status in June.

The companies and towns are concerned that a ruling in the case could have far-reaching implications for activities along the river.

To that end, the coalition is seeking a ruling from the court confirming that the reservation does not include any portion of the river, citing the State Settlement Act and the Federal Indian Claims Settlement Act of 1980.

The coalition members each hold federal permits authorizing them to discharge water or treated wastewater into the Penobscot River or its tributaries, court documents say.