The Aquinnah Wampanoag tribe on Martha’s Vineyard is speaking out against federal legislation that would create a sovereign reservation in Southeastern Massachusetts for their sister tribe, the Mashpee Wampanoags.

The Aquinnah Wampanoags sent a letter to the state Gaming Commission, complaining that they are not included in the bill introduced by Reps. Bill Keating and Joseph Kennedy.

The federal legislation was introduced after a court ruled the Interior Department didn’t have the authority to allow a reservation for the Mashpee tribe.

“While we remain empathetic to the legal challenges facing our sister tribe the Mashpee Wampanoag, as introduced, the legislation has the very real potential to have a serious adverse effect on our Tribe and our sovereign right to acquire additional lands in shared Wampanoag Ancestral territory within the Commonwealth of Massachusetts,” the tribe’s chairwoman, Cheryl Andrews-Maltais wrote in the letter. “Unless and until the legislation is amended to include our tribe, we must remain adamantly opposed to its introduction and passage and have relayed our position to members of Congress co-sponsoring the bill.”

Andrews-Maltais also emphasized that both the Aquinnah and Mashpee tribes are recognized as successors to the Great Wamapnoag Nation, which covered much of Southeastern Massachusetts. She says although the Aquinnah have a reservation on Martha’s Vineyard, three quarters of their population live on the mainland.

“This disbursement of tribal members makes maintaining the right and ability to acquire tribal trust land within this territory even more critical for the Aquinnah Wampanoag,” she wrote.

"Just because the reservation lands on Martha's Vineyard were awarded to them, doesn't mean that they don't have a valid claim, or at least a valid relationship, between their branch of the tribe, and lands that are also on the mainland as well," said Lasell College professor Paul Debole, who studies casino gaming and used to work for a lobbying firm representing the Aquinnah tribe.

The Aquinnah already have plans to open a gaming facility on the Vineyard.