Opponents of a nuclear power expansion in Georgia are suing over it. Environmental groups claim state regulators didn’t follow their own rules when they decided to let construction at Plant Vogtle continue.

In December, the Georgia Public Service Commission voted unanimously to keep work on two new nuclear reactors going, even though they’re five years behind schedule and billions of dollars over budget.

The groups Georgia Interfaith Power and Light and the Partnership for Southern Equity claim the commission rushed the decision and should have gathered more information.

“This was the wrong way to go about making a multi-billion dollar decision,” said Kurt Ebersbach, an attorney at Southern Environmental Law Center, who represents the groups.

The suit is being filed in Fulton County Superior Court.

The chairman of the Public Service Commission said he finds it “highly unlikely” the commission made any procedural errors.

“I believe this is just another way for their message to get out and say, ‘We’re opposed.’” Stan Wise said. “Well, message received. We know you’re opposed.”.

The expansion at Plant Vogtle is the only nuclear construction project in the country. Its future was up in the air for much of last year, after the lead contractor on the project went bankrupt.

Since then, there has been good news for the nuclear expansion, which is owned by Georgia Power and other Georgia utilities. Toshiba, the parent company of the now-bankrupt contractor, paid the utilities more then three billion dollars to cover its parental guarantee. The Department of Energy has said it will give Georgia Power additional loan guarantees. Last week, a deadline was lifted on federal tax credits that will benefit the project once it’s up and running.

There has also been mounting opposition. In addition to the groups that have long-opposed the project, some state lawmakers have gotten involved. There are two bills this legislative session that seek to curb how much money Georgia Power can collect from its customers on their monthly bills to put towards Vogtle.