A new group aimed at fighting a proposed $6.5 million luxury hotel on Great Diamond Island in Casco Bay has filed a lawsuit to halt the development.

The Friends of Great Diamond Island filed the suit in Superior Court in Portland against the Diamond Cove Homeowners Association and The Inn at Diamond Cove LLC, which is proposing the hotel, to invalidate a controversial vote last year by property owners on the island that removed barriers to the development, which would transform Fort McKinley's old barracks into a 36-room luxury hotel, according to a press release from The Friends of Great Diamond Island. The Friends of Great Diamond Island claim the vote was not valid because the City of Portland, which supports the hotel development, inappropriately influenced the vote. Because the city owns the property, which it acquired by foreclosure in 2004, it was able to tip the vote last year in favor of the development.

David Bateman, the developer behind Portland Harbor Hotel, and Hart Hotels, the Buffalo, N.Y.-based hotel development company that manages the Portland Harbor Hotel, are behind the proposed Inn at Diamond Cove. Bateman in the 1980s renovated other former fort buildings on the island into 77 homes, according to the Portland Press Herald.