For the fourth time in two years, the state Public Service Commission delayed a decision Tuesday on a proposal to trim Georgia Power profits if its Plant Vogtle nuclear expansion goes too far over budget.

The measure’s supporters questioned whether regulators really are in control of the issue.

Commissioner Stan Wise, who proposed the latest delay, said Georgia Power raised new accounting issues last week that will require the PSC to reopen hearings and examine new evidence on the cost-containment plan.

“It is important that we look at these issues,” Wise said.

“Georgia Power is gaming this commission,” said Stephen Smith, of the Southern Alliance for Clean Energy. “Its really challenging the fundamental premise of who’s in charge here.”

Angela Speir Phelps, who heads consumer group Georgia Watch, said the delay is “a second chance for the utility to raise new arguments.”

Georgia Power spokesman Jeff Wilson said the company didn’t raise the accounting issue earlier because it assumed the PSC staff would be aware of them.

At issue is how to deal with potential cost overruns as the heavy construction part of the $14 billion project to build new reactors inches closer.

Georgia Power customers began paying financing costs for the project in January, and will pay for the construction itself after the reactors are finished in 2016 and 2017.

The PSC has certified $6.1 billion as the utility’s allowed costs for the project, with the rest of the money coming from electric co-ops and city-owned power companies.

The staff proposal would shave Georgia Power’s allowed profit margin on the project if it runs more than $300 million over budget, and boost its allowed profits if it beats budget by the same amount. The utility would lose $300 million in profits on the reactors over a 30-year time period, for instance, if the project went $900 million over budget.

The utility says the proposal is illegal and unnecessary and would punish shareholders for cost overruns outside its control.

The PSC delayed action in 2009 and asked its staff and Georgia Power to come up with a compromise last summer. Only the staff submitted a proposal, which was on the table Tuesday.

Last week the company said the proposal would require parent Southern Co. to report all profits lost over the reactor’s life in one reporting quarter, skewing its financial results.