Coal power plant
Coal power plants are the largest source of greenhouse gas emissions in the USReuters

The US Supreme Court has dealt a serious blow to President Barack Obama's plans to boost environmental protections by temporarily blocking his administration's new regulation to limit greenhouse gas emissions from coal-fired power plants. The judges blocked the Clean Power Plan of the Environmental Protection Agency while the regulation is challenged in an appeals court in a lawsuit brought by 29 states, coal mine operators and utilities, arguing that the plan isn't realistic and infringes on states' rights.

Observers viewed the "stunning decision" by the top court as an indication that the Clean Power Plan could face a dim future if they end up back before the justices after the hearing. The 5-to-4 vote, with the court's four liberal members dissenting, was unprecedented.

The Supreme Court had never before granted a request to halt a regulation before review by a federal appeals court. The US Court of Appeals for the D.C. Circuit will hear oral arguments in the case against the Clean Power Plan in June.

"This is an exceedingly uncommon situation for the court to step in, and it jeopardises the plan all together from going into effect while President Obama remains in office," Bruce Huber, professor of law at Notre Dame Law school, told CNN. "The Supreme Court's order signals serious misgivings among some of the justices about the legality of the plan."

The new rules would require states to meet specific carbon emission reductions based on each state's specific consumption levels. States and industry operations wouldn't be required to hit the first reduction benchmarks for six years.

If allowed to stand the plan could transform the nation's electric power system, cutting emissions from existing plants by a third by 2030, and by closing hundreds of coal-fired plants and increasing production of wind and solar power. The president has pushed action on global warming as a key part of his legacy, which now may be tied up in the courts until he's out of office.

"Power plants are the single biggest source of harmful carbon pollution that contributes to climate change," Obama said when he announced the new plan. "Until now, there have been no federal limits to the amount of carbon pollution plants dump in the air."

The initiative was the administration's initial contribution to a historic climate change pact reached in Paris in December 2015 by 195 nations. As long as the programme is suspended, the US isn't upholding its part of the deal.

Republicans, states and the power industry were delighted with the decision. "We are thrilled that the Supreme Court realised the rule's immediate impact and froze its implementation, protecting workers and saving countless dollars as our fight against its legality continues," West Virginia Attorney General Patrick Morrisey told the New York Times.

Others were not so pleased. "If there was ever a Supreme Court decision that looked backwards instead of towards the future, this was it," said Jamie Henn of the environmental group 350.org.