As if Southern Co.’s Plant Vogtle problems weren’t enough, utility regulators are telling the Atlanta company’s Mississippi unit to pull the plug on its troubled “clean coal” plant and absorb billions in costs.

Mississippi Power’s Kemper plant was designed as a first-of-its-kind power plant that would burn coal more cleanly, but it is years past its planned completion date, billions of dollars over budget, and still not working properly.

The Mississippi Public Service Commission on Wednesday gave Mississippi Power 45 days to agree to a settlement of rate matters regarding the $7.5 billion plant. The regulators say Southern, Mississippi Power’s parent company, should absorb $6.5 billion in losses and ratepayers should pay nothing more.

The three elected commissioners say the plant should burn only natural gas, as it has mostly done since 2014. They also want rates to at least stay level for customers, and preferably go down.

Parts of the plant, originally projected to cost $2.9 billion, remain incomplete, more than three years behind schedule.

Georgia Power, Southern's largest subsidiary, faces similarly big headaches with its project to build two new nuclear reactors at Plant Vogtle near Augusta.

The Vogtle expansion is over three years behind schedule and more than $3 billion over budget. More costs and delays are expected after the project's key contractor, Westinghouse Electric, filed bankruptcy in late March.

Georgia Power is studying what to do with the half-finished project, ranging from shutting it down to converting to natural gas to continuing construction of the reactors.

But two recent developments may help clear the path for continued construction. Earlier this month Westinghouse's parent, Toshiba, agreed to pay $3.7 billion to cover losses on the project.

Wednesday, the House of Representatives voted to extend federal tax credits — $800 million for Georgia Power alone — that can be used by Plant Vogtle participants once the reactors are working. The tax credit extension still needs Senate approval to become law.

— The Associated Press contributed to this report.