Obama’s Clean Power Plan aims to cut carbon emissions by 32% before 2030 to help leverage a stronger global treaty to spur other major polluting countries such as China to adopt similarly aggressive policies.

Colorado Attorney General Cynthia Coffman said she was considering joining West Virginia, Oklahoma, Alabama and other states in a legal challenge against the Environmental Protection Agency, saying the Clean Power Plan raised “significant concerns” for the state.

“But as I put the best interests of Colorado first, it may become necessary to join other states in challenging President Obama's authority under the Clean Air Act,” she added.

Republican governors of several states have also threatened to not comply with the plan.

While Colorado’s Democrat Governor John Hickenlooper did not address Coffman’s threat, his spokeswoman Kathy Green said: "We respect the due diligence of the attorney general in reviewing the plan and will watch the next steps closely”

Hickenlooper said: “We realise these are ambitious goals and may be challenging for Colorado, but we have risen to these challenges before by developing a mix of cost-effective strategies across the energy spectrum.”

He told Senate Majority Leader Mitch McConnell on May 14 that Colorado intended “to develop a compliant Clean Power Plan" as required.

Colorado Department of Public Health and Environment director Larry Wolk said earlier this week that “from my standpoint and the governor's standpoint [the Clean Power Plan] is certainly something we support. It is the right thing to do”

He added that if there was a legal challenge to be had related to EPA authority, that would be a matter specific to the Attorney General.