But the Supreme Court in 2015 ruled that the EPA improperly failed to consider the costs of regulating power plants' emissions of hazardous air pollutants. Several years later, in 2023, the EPA determined after considering the costs that regulation of power plants is "appropriate and necessary," a standard set by the Clean Air Act.

The U.S. Supreme Court declined on Friday to put on hold new federal air pollution rules from President Joe Biden's administration to tighten limits on mercury and methane, acting in challenges brought by a group of states - most of them Republican-led - and industry groups.

The Supreme Court on Friday let stand Biden administration rules that would cut emissions of the planet-warming gas methane as well as mercury in a rare win for an environmental regulation pending before the conservative high court.

States and industry groups had asked the Supreme Court to pause the EPA's rule that aims to curb emissions of methane from new and existing oil and gas facilities.

The US Supreme Court refused for now to halt a Biden administration crackdown on planet-warming methane emissions from oil wells, tanks and pipelines.

The Supreme Court refused to block new Biden rules requiring fossil-fuel-fired power plants to slash emissions of toxic substances and oil and gas firms to curb methane from drilling operations.

Industry groups and Republican attorneys general argue the EPA overreached when imposing new rules to address one of the most potent greenhouse gases.

The methane rule puts new requirements on the oil and gas industry, which is the largest emitter of the gas that's a key contributor to climate change.