Two energy companies seeking the continued operation of a coal-fired power plant in Colstrip are asking the U.S. Supreme Court to block a federal emissions standard from taking effect.
Talen Montana and NorthWestern Energy this week requested that the Supreme Court halt a rule the U.S. Environmental Protection Agency adopted in April to limit airborne pollutants that are released when coal is burned for electricity.
The companies argue that complying with the EPA rule, paired with another rule that limits climate-warming carbon dioxide emissions, will force the plant to close.
“These two rules — taken together — put an untenable burden on Colstrip,” the filing reads. It goes on to describe a “stark choice” before Talen, which operates the plant, and NorthWestern Energy, which co-owns the plant with utilities in Washington and Oregon that are shifting away from coal-fired power.
NorthWestern and Talen wrote they can retire the plant by July 2027 or invest $350 million to comply with the Mercury and Air Toxics Standards. Even if the companies upgrade Colstrip, they maintain they will be forced to shutter the plant by 2031 when the greenhouse gas standard goes into effect.
“Either choice is both irreversible and highly consequential for Colstrip, its owners, and Montana,” the appeal reads. “Without a stay of the final rule, Colstrip’s owners are forced to make this decision without knowledge of the playing field. … Colstrip’s future should not depend on a rushed decision-making process while this case is pending. Potentially catastrophic outcomes can be avoided through a stay.”
The companies argue that closing Colstrip, which they describe as the largest coal plant operating west of the Mississippi, threatens grid reliability and increases costs for Northwestern Energy’s hundreds of thousands of customers. While the filings estimate the required MATS upgrade will cost $350 million, Talen earlier indicated that the price tag could top $600 million.
The companies are asking the Supreme Court to stay the MATS rule while a lower court considers the merits of multiple legal challenges that have been brought by states and industry groups.
Environmental and public health advocacy groups have supported the new EPA emissions standards, describing them as long overdue and protective of Montanans who live near and downwind of Colstrip.
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In an email to Montana Free Press, Montana Environmental Information Center Co-director Anne Hedges described NorthWestern and Talen as “shameless.”
“They are using ancient technology to prevent toxic air pollution instead of industry-standard controls. They whine about having to do what every other similar facility has already done to protect the public from lead, arsenic and other harmful pollutants,” she wrote. “They should have installed the technology decades ago when it was cheaper to do so, but they chose profits over public health.”
NorthWestern and Talen argue in their filing that anticipated public health benefits from the stricter standard are meager and that the existing standard is well within the agency’s safety margin for human and environmental health. They assert that the plant has been in compliance with the existing standard for “filterable fine particulates” — soot — since a 2018 incident, which was resolved after the plant underwent an upgrade.
“Colstrip’s future should not depend on a rushed decision-making process while this case is pending. Potentially catastrophic outcomes can be avoided through a stay.”
Colstrip operator Talen and co-owner NorthWestern Energy
Those arguments fall flat with Robert Byron, a retired internal medicine doctor who’s active with Montana Health Professionals for a Healthy Climate. Byron said the MATS rule is based on scientific evidence and will result in “almost immediate health benefits” to nearby communities.
Reducing levels of heavy metals like mercury, a neurotoxin, and arsenic, a carcinogen, should be a public health priority, Byron said. He added that exposure to fine particulates is linked to strokes, heart attacks and adverse outcomes for pregnant mothers and their young children.
“In the past, we did not know much about the impacts of air toxics on human health. Now there’s strong evidence about it, and if we can do something about it, we need to, rather than just ignoring it for the sake of profit,” Byron said.
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Montana petitions Supreme Court to block EPA’s new pollution standards
The Montana attorney general, along with 19 of his colleagues in other states, asked the nation’s highest court to order an emergency stay of a rule the U.S. Environmental Protection Agency adopted in April to curtail greenhouse gases emitted by fossil fuel plants.
NorthWestern Energy announces deal to acquire larger share of Colstrip power plant
NorthWestern Energy announced that it will acquire a large share of the Colstrip power plant from Puget Sound Energy, a Washington-based utility facing a mandate to stop using coal-generated power by 2025.
The Montana Department of Justice has joined 22 other Republican states and a coalition of energy and mining industry groups in a separate appeal to the Supreme Court to stay the MATS rule.
The states’ filing argues that the EPA has evaluated the expected costs to comply with the rule — $860 million — without demonstrating “whether there are any resulting benefits to public health.”
Uncertainty surrounding the MATS rule and the greenhouse gas rule has also played out amidst uncertainty in the plant’s ownership. Late last month, NorthWestern announced an agreement with Puget Sound Energy, a Washington-based utility, to acquire its share of generation from Colstrip on Jan. 1, 2026. With that increased ownership share comes a larger share of expenditures related to maintenance for the nearly 40-year-old plant.
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