Mohegan Sun is suing Massachusetts gambling regulators over their decision to award the Boston-area casino license to a rival.

The Connecticut-based casino company is joining a Superior Court lawsuit filed late last year by the city of Revere and a labor union representing workers at the Suffolk Downs horse racing track.

Mitchell Etess, CEO of the Mohegan Tribal Gaming Authority, said Wednesday the company has never filed suit to challenge a casino license decision, but felt compelled to in this case because of the many issues around the what he called a "gravelly flawed" decision.

The lawsuit seeks to vacate the Massachusetts Gaming Commission's decision to award the license to Wynn Resorts, which plans a casino in Everett.

Mohegan Sun had proposed a resort at Suffolk Downs in Revere.