The head of a national group representing state air regulators is warning Senate Majority Leader Mitch McConnell to stop urging states to not comply with the Obama administration's power plant rules.

Bill Becker, the long-time head of the National Association of Clean Air Agencies, told a room full of agency officials, congressional staff and others at a Friday briefing that he would remind the Kentucky Republican "this is the law."

Becker said the consequences of the Republican leader's call for states "to stand down and ignore implementation" would be "severe."

If states don't comply with the rule, known as the Clean Power Plan, they would invite the government to implement a federal compliance plan for them, which "will be more expensive" and less flexible — ultimately making it worse for them than if they developed their own strategy — Becker said.

The Environmental Protection Agency proposed the Clean Power Plan in June 2014 and was sent earlier this week to the White House Office of Management and Budget for final review before being implemented in August.

The regulations are the centerpiece of President Obama's climate change agenda and have been met by strident opposition from GOP lawmakers. The rules are being challenged by 14 states that are suing the agency in federal appeals court.

The plan directs states to reduce their emissions by setting specific targets that each state must begin meeting in 2020, dubbed the compliance "cliff." States must begin submitting plans to EPA beginning next year.

The structure of the power plant rules are unprecedented, directing states — not utilities — to develop plans to reduce emissions. Many states say they would be unable to meet the interim 2020 target because of the heavy lift in planning and infrastructure development it would take. The EPA is expected to change the target in the final rule.

States also argue that the EPA rules, meant to limit emissions from existing power plants, are unconstitutional and exceed the agency's authority. McConnell and others also say that rules would cause electric prices to rise and make the power system more susceptible to outages and blackouts.

"I don't want to leave an impression that implementation … [is] a slam dunk," said Becker, because "it's not." But in the year since the Clean Power Plan was proposed, the nation's state environment and air quality regulators — charged with developing the states' implementation plans under the rules — have been engaged in "very good discussions … even with the states suing EPA."

At this point, applying the brakes would be counterproductive, he said. Becker's group has aligned itself with two other national groups representing state utility regulators and the governors' energy offices.

Just recently, the groups issued a nearly 500-page manual of sorts that outlines every option for complying with the Clean Power Plan. Becker said they will issue a compliance modeling tool 30 days after the climate rules are finalized.

Despite Becker's bullishness, senior officials from the other two groups aligned with the air regulators said they have not taken an official position on the EPA plan, underscoring the fact that not all their members agree with the emission rules.

Nevertheless, they repeatedly said that regulators from states that are fighting the rule in court are showing up to regional meetings, participating in compliance workshops, and attending meetings meant to negotiate a multi-state compliance framework.

Charles Gray, executive director of the National Association of Regulatory Utility Commissioners, said his group has been developing reports on how states can form multi-state compliance plans.

He said meetings on developing such a plan have been attended by more than 40 states. Gray said that shows that "even if you don't like it," states should do it in lieu of the federal option.

Gray also said his group wants implementation of the rule to keep rates affordable for consumers and will be vigilant in making sure the lights stay on.

David Terry, executive director for the National Association of State Energy Officials, said, "Air quality is serious business," but his members want to make sure it isn't impossible to achieve. His group is working with a number of states to create a national energy-efficiency registry to help states account for efficiency in complying with the rules.