A federal judge has ruled that the state and the Mashantucket Pequot and Mohegan tribes can intervene alongside the U.S. Department of the Interior in a 2019 lawsuit MGM Resorts filed against the Interior in a last-ditch effort to upend the tribes’ East Windsor casino project.

In a 15-page decision filed Wednesday in U.S. District Court for the District of Columbia, Judge Rudolph Contreras does not address the interveners’ claim that because they are sovereign entities with legal immunity, their being added to the suit means the suit must be dismissed.

“At the moment, the Court considers only whether this limited intervention should be allowed,” Contreras wrote.

The state and the tribes had argued they were “indispensable” parties to MGM’s suit, which alleges the Interior Department approved the tribes’ amended gaming agreements with the state in violation of the Administrative Procedure Act and the Indian Gaming Regulatory Act. The Interior approvals appeared to finally clear the way for the tribes to proceed with their long-stalled Tribal Winds Casino project, which the state authorized in 2017.

MGM has sought to block the project since 2015, fearing the competitive impact it could have on MGM Springfield, the nearly $1 billion casino MGM opened in western Massachusetts in 2018.

Tribal Winds, a roughly $300 million facility, would be built off Interstate 91 in East Windsor, some 12 miles south of MGM Springfield. The tribes proposed it as a hedge against MGM Springfield’s impact on Foxwoods Resorts Casino and Mohegan Sun, their southeastern Connecticut heavyweights.

With the gaming industry struggling to cope with the coronavirus pandemic, the tribes’ commitment to the Tribal Winds project was difficult to assess Thursday. A spokesman for MMCT, the joint venture the tribes formed to pursue the project, said they declined to comment on the latest development in the MGM suit or the project in general.

MGM Resorts did not immediately respond to a request for comment.

The tribes said a year ago that they had invested nearly $20 million in the East Windsor project and had no intention of abandoning it. At the time, Gov. Ned Lamont was urging them to refocus their expansion efforts in the state elsewhere, such as on Bridgeport or Hartford.

In his decision, Contreras wrote that the parties to the lawsuit may file briefs regarding the interveners’ sovereign immunity argument before he rules on their motion to dismiss the case. He also has yet to rule on a separate dismissal motion filed by Interior.

The motions were filed in October 2019.

b.hallenbeck@theday.com