HARTFORD — A federal court judge sided Thursday with the state in a suit over the expansion of casino gambling in Connecticut, dismissing a complaint that a law excludes all but the operators of Foxwoods and Mohegan Sun from opening a third casino.

MGM Resorts International, the developer of a $950 million casino and entertainment complex in Springfield, challenged a state law that allowed the Mashantucket Pequots and Mohegans to seek a location off their reservations for a jointly-run, "satellite" casino. MGM argued the law violated constitutional rights of equal protection, excluding MGM and other commercial developers from competing for a piece of the Connecticut gaming market.

In a 20-page decision, U.S. District Court Judge Alvin Thompson said the law, enacted in 2015, does not favor the tribes "to the detriment of other entities against whom it may be competing, like MGM."

"The act does not establish a process to be followed by everyone who wants to develop a proposal for and petition the General Assembly to authorize a casino gaming facility, nor does it provide that only the tribes can do so," Thompson wrote.

The legislation simply outlines the procedural steps that the tribes must take to establish the gaming venue in Connecticut, Thompson wrote.

Attorney General George Jepsen argued that the lawsuit should be dismissed, given there was nothing in the legislation that prevented MGM from also seeking authorization to open a casino in Connecticut.

"Our office is reviewing the court's ruling, but we are pleased that the motion was granted," Jaclyn Falkowski, a spokeswoman for Jepsen, said. "We will continue to defend this case against any appeal that may be filed."

MGM reacted swiftly to the ruling Thursday, promising that it had no intention of abandoning its fight.

"While we respect the court, we fundamentally believe the opinion was incorrect and we will immediately seek an expedited appeal," Alan Feldman, MGM's executive vice president of global government & industry affairs, said.

In his decision, Thompson acknowledged the legislation required that the tribes' joint venture, MMCT, post a "request for proposals" on the state Department of Consumer Protection website, MGM "failed to allege facts sufficient to support an inference that DCP doing so is barrier to MGM competing on an equal footing."

The tribes are now permitted by state and federal governments to operate casinos on their reservations in Uncasville and Ledyard in southeastern Connecticut.

The push for a casino in the Hartford area is intended to blunt the competitive pressure from MGM's $950 million casino and entertainment complex, now under construction in Springfield and expected to open in the fall of 2018. The effort has been framed as a strategy to keep more gaming dollars in Connecticut, preserving jobs at Foxwoods and Mohegan Sun and slot revenue, a portion of which goes monthly into state coffers.

The 2015 legislation did not authorize the tribes to expand off their reservations for the state's first commercial casino, just seek out locations. The tribes must come back to the legislature with a location for final approval.

A spokesman for MMCT referred questions Thursday to the attorney general's office.

Rep. Stephen D. Dargan, D-West Haven, co-chairman of the legislature's public safety committee, which oversees casinos, called the lawsuit "laughable" when it was filed in August.

On Thursday, Dargan said he wasn't surprised by Thompson's ruling.

"From the beginning, I didn't think MGM had any grounds," Dargan said. "But I'm sure there is going to be a lot of other litigation."

Dargan said the stakes are high for MGM. If the Mashantucket Pequots and Mohegans are successful in establishing a casino in the Hartford area, the venue will be just 15 or so miles from Springfield.

In addition to pursuing its own lawsuit, MGM is bankrolling a similar suit by the Kent-based Schaghticoke Tribal Nation. The attorney general also is trying to get that lawsuit dismissed as well.

This week, The Courant also reported that MGM had unsuccessfully pursued federal legislation that would have prevented tribes from establishing gaming operations off their reservations.