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 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.

The Supreme Court is refusing to hear several cases challenging the Environmental Protection Agency’s authority to implement two rules meant to reduce toxic emissions from the oil and gas industry.