Indiana Gov. Mike Pence says his state won't comply with the Environmental Protection Agency's effort to curb carbon dioxide from power plants—unless the administration dramatically overhauls its regulation.

Mike Pence sent a letter to the President Obama on Wednesday with that warning, saying that unless proposed EPA regulations for power plants are significantly "improved" before the agency finalizes them, Indiana will buck the rule.

That declaration arrives on the heels of a major push from Senate Majority Leader Mitch McConnell urging governors not to comply with the regulations, which stand at the heart of Obama's effort to tackle global warming and shore up a legacy on the environment before he leaves office.

In his letter to the White House, Pence did not explicitly outline what changes he hopes to see from EPA, but claimed that the regulation "fails to strike the proper balance between the health of the environment and the health of the economy," and warned that it will drive up the cost of electricity.

"As Governor of Indiana, I am deeply concerned about the impacts of the Clean Power Plan on our state, especially our job creators, the poor, and the elderly who cannot afford more expensive, less reliable energy. I reject the Clean Power Plan and inform you that absent demonstrable and significant improvement in the final rule, Indiana will not comply," Pence wrote, adding that Indiana will "reserve the right to use any legal means available to block the rule from being implemented."

Indiana joined a coalition of states that sued the administration in a failed effort to block the regulations before they were made final.

And this is not the first instance when a Republican governor has pushed back against the rule.

Oklahoma Gov. Mary Fallin signed an executive order blocking her state from complying with the power-plant regulations. Wisconsin Republican Gov. Scott Walker, a 2016 presidential prospect, has also vowed to fight the regulations in court. 

But if states don't comply, that's not the end of the story.

The administration plans to release a federal implementation plan that will direct states to achieve required emissions cuts if they fail to submit their own plans.

"Called for by President Obama's Climate Action Plan, EPA's approach is built on a time-tested state-federal partnership in the Clean Air Act, which was established by Congress, for EPA to establish public health goals and then gives states important flexibility to design plans to meet their individual and unique needs," Melissa Harrison, a spokeswoman for EPA, said in response to the letter.

This story has been updated.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.