The challengers contended that the Obama administration exceeded its authority under the Clean Air Act, the key law that addresses air pollution. More than a dozen other states and the National League of Cities, which represents more than 19,000 U.S. cities, filed court papers backing the rule.
Jeff Holmstead, a lawyer for coal-powered utilities that challenged the rule, said the court has never before blocked an EPA rule. "To say it's unusual is a bit of an understatement," Holmstead added.
Sean Donahue, a lawyer for environmental groups that support the law, said the court action was "surprising and disappointing." He added that "we remain very confident in the legal and factual foundations for EPA's rule."
Sam Adams, U.S. climate director for the World Resources Institute, said fighting to uphold the rule is important to ensure the Paris agreement stays intact.
"The benefits of the Clean Power Plan are definitely worth fighting for, not only for the United States but the high expectations it hopes to set internationally," he said.
(Reporting by Lawrence Hurley and Valerie Volcovici; Editing by Will Dunham and Lisa Shumaker)