The Massachusetts Gaming Commission has backed a plan allowing MGM Springfield to begin construction on its proposed $950 million casino.

The unanimous vote Thursday starts an environmental regulatory process allowing MGM Springfield to start the work.

The Gaming Commission voted in August to allow MGM Springfield to open in September 2018, more than a year after it was first awarded the resort casino license.

MGM Springfield has proposed reducing the size of the project - a six-story, rather than 25-story, hotel - while increasing the cost from $800 million. The project's overall square footage has been reduced.

Proposed design changes must be approved by Springfield city officials and the Gaming Commission.

The five-member Gaming Commission plans a separate vote on the design changes at a later date.