With a hearing scheduled in U.S. district court Monday in a complicated lawsuit over casino rights, the town of Aquinnah Tuesday filed a motion to intervene in the case to protect the town’s position that the Wampanoag Tribe of Gay Head (Aquinnah) does not have the right to build a gaming facility on the Island. With the filing, the town became just one participant in a tangled lawsuit involving a casino developer, the governor, the Massachusetts gaming commission, the Aquinnah Wampanoags, the Wampanoag Tribe of Mashpee — and now the town. At the heart of the issue is who has the right to build a casino in southeastern Massachusetts. The Aquinnah selectmen met Monday morning in executive session to decide whether to intervene in the lawsuit. Town administrator Adam Wilson said the vote by the board was unanimous to instruct town counsel Ronald H. Rappaport to file a motion seeking to intervene.

Two of the three selectmen are members of the Aquinnah Wampanoag tribe.

The initial lawsuit, filed by KG Urban Enterprises against Gov. Deval Patrick and the Massachusetts Gaming Commission, challenges a state law that gives American Indian tribes first rights to a casino license in southeastern Massachusetts.

KG Urban, a commercial casino developer, contends that the law is “racial-based” and unconstitutional.

Meanwhile, the Aquinnah tribe and the Aquinnah Gaming Corporation filed a motion in September to intervene in the lawsuit, saying that the result of the lawsuit could affect the tribe’s rights to build a casino.

The Aquinnah tribe had sought to

acquire one of the casino licenses, but the state refused to negotiate with them, saying that they had waived their sovereign rights in a land settlement agreement in the 1980s. In July, the governor entered into a compact agreement with the Mashpee Wampanoags to build a casino in Taunton. The compact was rejected by the U.S. Department of the Interior in October, but the Patrick administration and the Mashpees said they would renegotiate.

The Aquinnah tribe has since pursued plans to covert a tribal community center to some kind of gaming facility.

The Aquinnah/Gay Head Community Association, a taxpayer association, had filed a motion to intervene in the lawsuit to oppose the Aquinnah plans, and the Mashpee Wampanoags have also filed a motion to intervene in the case.

In Tuesday’s court filing, Mr. Rappaport said the town filed its motion to intervene when it learned that the court had set a hearing date to determine whether the other parties will be allowed to intervene.

“The town did not move to intervene earlier because, as a small municipality with a limited legal budget, it did not wish to expend its scarce financial resources in the event this court denied the Aquinnah tribe’s motion,” a memorandum filed with the court stated.

On Thursday, selectman and board chairman Spencer Booker said his board met to discuss the litigation because the judge scheduled a hearing.

“The tribe is looking to build a casino in the town of Aquinnah and so, as the town has in the past and as it’s looking to do again, is to hold the town accountable to the settlement agreement signed 25 years ago,” Mr. Booker said. “That’s the impetus and that’s why we [are seeking to join the lawsuit].”

Court filings outlining the town position state that a 1983 settlement agreement and a 2007 land use agreement would bar the tribe from commercial gaming in Aquinnah.

“The town qualifies for intervention as a matter of right because the Aquinnah tribe’s arguments, if successful, would eviscerate the settlement agreement to which the town is a party and has an obligation to enforce,” Mr. Rappaport wrote.

The hearing is set for 3 p.m. Monday in federal court in Boston.