Connecticut’s two U.S. senators are urging the Department of Interior to clarify that a joint casino venture between the Mohegans and Mashantucket Pequot tribes planned north of Hartford complies with a gambling compact with the state.

The agency hasn’t ruled one way or another on the legality of the project, creating a degree of uncertainty for the tribal owners of Mohegan Sun and Foxwoods as they look to build a casino in East Windsor to compete with an MGM resort that is scheduled to open next year in Springfield, Mass.

MGM is challenging the tribes’ exclusive rights to develop a third casino in the state and have unveiled plans for a $675 million privately funded waterfront casino in Bridgeport.

Democrats Richard Blumenthal and Chris Murphy, along with U.S. Rep. Joe Courtney, D-Conn., wrote to Interior Secretary Ryan Zinke Nov. 2 asking the agency to review and sign off on changes to the tribes’ existing compact with the state.

“The genesis of the compact amendments is the desire of the state of Connecticut to authorize an additional casino operation within Connecticut borders,” they wrote. “This is a decision based on the state’s review of its gaming policies, the impact on the people of Connecticut and the state budget.”

MGM officials say that the absence of a formal approval by the Interior Department, the parent agency of the Bureau of Indian Affairs, constitutes a denial.

They pointed to a recent opinion by state Attorney General George Jepsen, in which his spokeswoman said that going ahead with the project would pose “grave potential risks to the state of Connecticut.”

“(This) letter raises no new issues and provides no new information that would change the Department of the Interior’s decision not to approve the tribes’ submissions,” said Uri Clinton, senior vice president and legal counsel for MGM Resorts International. “It also does not address the risks to the state of proceeding with (tribes’) proposed casino without Interior approval that have been emphasized by Attorney General Jepsen’s office.”

The tribes plan to start work on their new casino, which will have 3,000 slot machines and 50 to 150 table games, by year’s end with the demolition of a former multiplex cinema on the site off Interstate 91.

They say that a Sept. 15 deadline came and went without the Interior Department raising objections.

In the 1990s, the state entered into a compact with the Mashantuckets and Mohegans giving them exclusive casino rights in return for them forking over 25 percent of annual slot machine revenues to the state.

The state’s cut of casino taxes has fallen precipitously from $430 million in 2007 to $260 million because of the economic downturn and casino competition in New York and Massachusetts, however.

MGM , represented by former U.S. Attorney General Eric Holder, unsuccessfully sued the state over what it claims is an unfair monopoly. It has vowed further litigation after its most recent challenge was denied by the Second Circuit Court of Appeals in New York City.

The Legislature and the governor would have to reopen the approval process that gave the tribes the green light to open their joint venture casino.

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