The Obama administration used the one-year anniversary of President Obama's climate regulations to tout their strong legal standing ahead of oral arguments in federal court next month.

The Environmental Protection Agency's "charge from the president was clear: to exercise our statutory authority to lay out steady, responsible steps to cut carbon pollution under the Clean Air Act," said EPA Administrator Gina McCarthy in a Wednesday blog post. "And that's what we did — by setting limits that reflected the growing momentum in the power sector to provide the American public with cleaner sources of energy."

The plan is being opposed by nearly 30 states and dozens of industry and trade groups that say it oversteps the federal government's authority to regulate carbon emissions from existing power plants. Although it targets power plant emissions in an effort to fight climate change, it actually requires individual states to reduce greenhouse gases a third by 2030.

The D.C. Circuit Court of Appeals is scheduled to hear an oral argument in the case on Sept. 27. The Supreme Court stayed the regulation in February until all court action has finished.

"Sometimes our efforts to protect public health and environment face opposition and/or litigation," McCarthy added. "The Clean Power Plan is no different and was stayed by the Supreme Court until the litigation is resolved. However, it will see its day in court and EPA remains fully confident in its legal merits."

She said that although the plan was halted by the high court, many states have expressed their resolve to continue moving forward voluntarily. "They have asked the agency to continue to develop tools to support them in their voluntary efforts. We are doing just that," she said.

The agency began a round of public hearings in Chicago on Wednesday to hear from industry groups and others on a voluntary proposal to incentivize the development of renewable energy in line with the Clean Power Plan's goals. Critics and GOP lawmakers have criticized the proposed incentive program as an affront to the Supreme Court's stay.

Sen. Lamar Alexander, R-Tenn., chairman of an appropriations committee energy panel, sent a letter to McCarthy Tuesday criticizing the Clean Energy Incentive Program for picking "winners and losers" by choosing solar and wind resources over zero-emission nuclear power plants. Nuclear is the second-biggest source of power in his state, behind coal.

Nuclear energy is "this country's largest source of clean electricity," Alexander said. "Nuclear power provides over 60 percent of our carbon-free electricity and is available 92 percent of the time," he told McCarthy. "Wind provides only 15 percent of our carbon-free electricity, and that's only when the wind blows — which is only about 35 percent of the time, according to the U.S. Energy Information Administration, and usually occurs at night, when we don't need more electricity.

"If reliable, cheap and clean electricity is the goal, then nuclear energy should be incentivized instead of giant wind turbines that produce a puny amount of electricity at a great cost to taxpayers," he added in the letter.