A federal regulation that has major implications for the continued operation of Montana’s largest coal-fired power plant in Colstrip remains in effect as the U.S. Supreme Court declined to take immediate action on a legal challenge.The country’s highest court on Friday denied petitions brought by Republican states and energy industry groups seeking a stay of the Mercury and Air Toxics Standard while the D.C. Circuit Court of Appeals weighs the merits of legal challenges to the five-month-old rule.The U.S. Supreme Court’s decision not to block the MATS rule from going into effect compresses the timeline for Colstrip’s six co-owners to decide if they’re going to shutter the nearly 40-year-old plant or invest hundreds of millions of dollars in upgrades to meet the U.S. Environmental Protection Agency’s 2028 compliance deadline.The EPA adopted the MATS rule in April to reduce airborne emissions of toxic heavy metals such as lead, arsenic and mercury. The EPA’s adoption of the rule was cheered by environmental and public health advocates who have long called for Colstrip to invest in the kind of pollution controls that have been adopted by virtually every other large coal plant operating in the U.S. In recent conversations with MTFP, Robert Byron of Montana Health Professionals for a Healthy Climate highlighted the link between heavy metals and cancer risk as well as fine particulate matter and strokes, heart attacks and adverse health outcomes for pregnant mothers and their young children.“Like all EPA standards, the MATS rule is based on scientific evidence supporting public health,” Byron said in a press release celebrating the Supreme Court’s recent order. “By allowing the rule to continue to be enforced, the Supreme Court highlights the importance of protecting the health of Americans.”In seeking the Supreme Court’s intervention, Montana and its co-plaintiffs had argued that the MATS rule “will impose tremendous costs and risk destabilizing the nation’s power grids without creating any relevant or quantifiable benefit to public health.” The Montana Department of Justice did not respond to MTFP’s request for comment on the U.S. Supreme Court order by press time Friday.The Montana Environmental Information Center described the Supreme Court’s order as a “victory for our constitutional right to breathe clean air.”“Now that the U.S. Supreme Court has stated that the MATS clean air rule can move forward, NorthWestern Energy must finally plan to address its serious pollution problem at the Colstrip coal-fired power plant,” MEIC deputy director Derf Johnson wrote in a press release. “It can no longer pretend that lead and arsenic aren’t harming public health.” NorthWestern Energy, Montana’s largest power company and one of Colstrip’s six co-owners, has previously indicated that the MATS rule, paired with another EPA rule related to greenhouse gas emissions, could make continued plant operation “uneconomic.” It has, however, recently suggested to Montana lawmakers that the required upgrade pencils out and is asking utility regulators to approve a new tariff that aims to secure funding for the upgrades from its customers.In its petition to the Supreme Court, NorthWestern and Talen Montana, a plant co-owner that also oversees its day-to-day operations, had argued that the MATS rule put an “untenable burden” on Colstrip and that “potentially catastrophic outcomes can be avoided by a stay.”In an emailed statement to Montana Free Press, NorthWestern spokesperson Jo Dee Black said the MATS rule challenge “is not over,” as briefings in the D.C. Circuit Court of Appeals are ongoing. Earlier this year, the circuit court ruled that an emergency stay to halt the rule was not warranted because the plaintiffs had not satisfied “the stringent requirements for a stay pending court review.”The post U.S. Supreme Court declines to block emissions rule that requires Colstrip upgrades  appeared first on Montana Free Press.