The Aquinnah/Gay Head Community Association this week joined the Wampanoag Tribe of Gay Head (Aquinnah) in trying to insert the question of the Vineyard tribe’s right to build a casino in Massachusetts into a broader federal lawsuit.

Attorneys for the taxpayer association say they want to protect their right to oppose any casino and to uphold a negotiated land claims settlement agreement that the tribe signed with the town and the taxpayers in 1983. That agreement paved the way for federal recognition of the tribe and is at the center of the tribe’s dispute with the state over its refusal to negotiate a compact for a casino.

Meanwhile, the private developer who filed the underlying lawsuit challenging the constitutionality of the Massachusetts casino law argued Wednesday that the Aquinnah tribe is trying to hijack an unrelated case for its own purposes.

KG Urban, which wants to build a casino in New Bedford, has sued Gov. Deval Patrick and the state Gaming Commission, contending that the state’s casino law passed last year, which set aside one of three licenses for a federally recognized Indian tribe, gave unfair preference to a racial group. The case is currently back before a U.S. District Court judge in Boston after an earlier decision was overturned by a federal appeals court.

“The Aquinnah tribe now seeks to divert [this] suit in order to litigate complex and wholly unrelated issues involving whether the Aquinnah tribe waived their right to engage in gaming as part of a settlement of land claims in the mid-1980s,” attorneys for the developer said in a nine-page brief. “If the Aquinnah believe they have been wronged by the commonwealth’s refusal to negotiate a gaming compact, they have a number of different avenues through which they can seek relief.”

KG Urban’s sights are focused on the Wampanoag Tribe of Mashpee, which successfully negotiated a compact this summer with the state for the exclusive right to build a casino is southeastern Massachusetts. The compact must be approved by the U.S. Department of the Interior and the Mashpee tribe is now seeking approval from the Bureau of Indian Affairs to acquire trust lands to build a casino in Taunton.

In a separate filing Wednesday, KG Urban called the state’s compact “a race-based regional gaming monopoly to a single landless tribe — the Mashpee Wampanoag.”

The motion by the Aquinnah tribe to intervene in the case must be still be approved by the presiding judge, who had given both KG Urban and the state until Wednesday to argue for or against allowing the Vineyard tribe in.

While the developer strenuously objected to the Aquinnah tribe’s involvement, the state said, in a short brief filed Wednesday, that it took no position on the tribe’s bid to take part. In a separate document, the state argued that KG Urban’s lawsuit should be put on hold until the Bureau of Indian Affairs decides on the Mashpee’s land trust issue.

KG Urban submitted its own proposal laying out a schedule that could resolve the case by next spring.

In explaining the Aquinnah taxpayer group’s interest in intervening, Felicia H. Ellsworth, an attorney with Wilmer Hale in Boston, said the group was simply protecting its interest in defending the 1983 settlement agreement.

“The tribe faces many hurdles in making the argument that the negotiated terms of the settlement agreement — in which the tribe received exclusive use of hundreds of acres of publicly and privately-owned land in exchange for relinquishing its aboriginal title and claims — do not mean what they say,” she wrote. “However unlikely it may be that the tribe will succeed in these arguments, if the court permits the tribe to intervene . . . the AGHCA respectfully requests it, too, be permitted to intervene to defend the terms and existence of the settlement agreement.”

The agreement was upheld by the Massachusetts Supreme Judicial Court in a landmark ruling in 2004. The tribe is claiming that the federal Indian Gaming Regulatory Act supersedes the agreement.

“The motion hits right at our settlement agreement because it basically says the Indian Gaming Regulatory Act supersedes [the state law],” association president Larry Hohlt told the Gazette. “We don’t believe that.”

“We worked long and hard to bring a settlement agreement together and whenever it is threatened, in or whole or in part, it’s something we have to become involved in,” he said. “We will always take steps to uphold the settlement agreement and make sure it is interpreted and applied appropriately.”

The town of Aquinnah has not filed a motion to intervene in the case, but the town selectmen went into executive session with their town counsel last week to discuss pending litigation involving the legal situation around the tribe.