The Mohegan and Mashantucket Pequot tribes, rivals for nearly four centuries, convened last week to declare further action against encroaching economic competition: the $800 million casino under construction in nearby Springfield, Massachusetts.

Council members of both tribes, along with labor union leaders and Lt. Gov. Nancy Wyman, assembled Sept. 10 in Hartford to formalize a joint venture to select a site for Connecticut’s third casino. The venture, which was filed on Aug. 24 with Secretary of the State Denise Merrill, is the latest step in a move to protect revenue and jobs from rival MGM Resorts International’s casino under construction just under seven miles from Connecticut’s northern border. The venture seeks to open the new casino near Springfield, in the region north of Hartford along I-91.

“This is a proud moment because it emphasizes how we are working for a common goal in mind: the welfare of Connecticut’s workforce,” Rodney Butler, chairman of Mashantucket Pequot Council, said at the signing ceremony commemorating the partnership between the two tribes.

The jointly-run casino seeks to reclaim 3,000 jobs and $6 to $7 million in revenue that the Springfield casino will drain from Connecticut’s current gambling operations, according to Butler and Mohegan tribal council chairman Kevin Brown.

A study sponsored by the tribes found that the state could lose as many as 9,300 jobs and $703 million in revenue from gambling operations by 2019 if no proactive measures are taken against the Springfield casino.

Currently, the Mohegan and Mashantucket Pequot tribes each manage their own casinos in Connecticut — the Mohegan Sun and Foxwoods Resort Casino, respectively — both of which reside on reservation lands. If approved, the third casino would be regulated by the state and jointly controlled by the two tribes. A share of the revenues would go to the state, while the two tribes would share the remaining earnings. In late May, the General Assembly negotiated a bill that enabled the tribes to begin discussions with communities interested in housing the new casino. But a public letter of concern from state Attorney General George Jepsen led the assembly to hold off on authorizing the casino. Development of the casino cannot begin without further approval from the General Assembly.

In his letter, Jepsen voiced skepticism of the original bill, which authorized a new casino. He alleged that an exemption from Connecticut anti-gambling laws — which prohibit gambling on all lands other than tribal reservations — could constitute a violation of the 14th Amendment’s Equal Protection Clause. Additionally, he questioned whether opponents of the bill might challenge its constitutionality under the Commerce Clause.

“The proposed legislation raises several legal issues that cannot be resolved with a high degree of certainty,” Jepsen wrote.

Swayed by the attorney general’s cautionary letter, the legislature opted not to vote on the bill this spring, instead passing a watered-down version which permitted the tribes to begin galvanizing local support for the project. Still, leaders in towns such as East Hartford, East Windsor and Enfield have already voiced interest in the state’s third casino.

A recent federal lawsuit by MGM against the state encapsulates both of Jepsen’s concerns. The suit claims that the act passed in May excludes groups outside of the Mohegan and Mashantucket Pequot tribes.

Senate Chief Deputy Minority Leader John Kissel, a Republican who represents Enfield, expressed serious concerns regarding the potential outcome of a legal battle.

“A lawsuit could lead to the opening up of casinos to all tribes in our state, as well as to private corporations,” Kissel said in a statement last Thursday. “A lawsuit could lead to the loss of the revenue the state currently receives from the tribes. Is that the path we want to go in Connecticut?”

Brown stressed last week that the scope of the project has not changed since its initial announcement last spring, citing an investment of $200 to $300 million for the construction of the property. He added that the new casino would house approximately 2,000 slot machines, along with 100 to 150 gambling tables.

Union support of the new casino became apparent last week at the signing ceremony when union director Julie Kushner declared a “coalition of unions” backing the venture, including the Service Employees International Union and the United Food and Commercial Worker’s Union. Kushner serves as director of United Auto Workers Region 9A, which represents nearly 2,000 workers at the Foxwoods Resort Casino.