By Andrew Chung, John Kruzel
WASHINGTON (Reuters) -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 justices denied emergency requests by the states, as well as power and mining, oil and gas companies, to halt the Environmental Protection Agency rules while litigation continues in lower courts.
The regulations, issued under the landmark Clean Air Act anti-pollution law, aim to cut mercury and other metals from coal-fired power plants emissions, as well methane and other gases known as volatile organic compounds from oil and gas production.
The mercury rule tightened limits on emissions of toxic metals for all coal plants by 67% and tightened limits on mercury emissions from lignite coal plants by 70%.
The methane rule restricted flaring - the burning of excess methane during oil and gas production - and required oil companies to monitor for leaks from well sites and compressor stations. It also created a new program for detecting and reporting large methane releases from so-called "super emitters."
The challengers contend that the EPA exceeded its powers in issuing unjustified rules that threaten the U.S. electricity supply and usurp the role of states in establishing emissions standards.
The regulations would benefit public health and the climate, the EPA said.
The mercury rule reduces the risk of heart attacks and cancer caused by such pollutants, as well as developmental delays in children, while reining in methane, which has more warming potential than carbon dioxide and breaks down in the atmosphere more quickly, can have a more immediate impact on limiting climate change, according to the EPA.
Challengers including the states, fossil-fuel industry groups, as well as power, mining and oil and gas companies filed multiple lawsuits in the U.S. Court of Appeals for the District of Columbia Circuit, which in July and August denied requests to pause the regulations pending its review.
The Supreme Court, which has a 6-3 conservative majority, has restricted the powers of the EPA in some important rulings in recent years.
In June, the court blocked the EPA's "Good Neighbor" rule aimed at reducing ozone emissions that may worsen air pollution in neighboring states. In 2023, the court hobbled the EPA's power to protect wetlands and fight water pollution. In 2022, it imposed limits on the agency's authority under the Clean Air Act to reduce coal- and gas-fired power plant carbon emissions.