The Environmental Protection Agency did not have clear direction from Congress to require power plants to shift from coal to cleaner energy sources, the Supreme Court said in a decision Thursday that could hamstring the agency’s efforts to adopt regulations addressing climate change.

But the court’s landmark 6-3 ruling also could have more far-reaching effects as federal agencies interpret other laws whose language may not provide clear guidance.

The decision in West Virginia v. EPA concerns the Clean Power Plan, an Obama-era rule that mandated “generation shifting” at power plants. The CPP never went into effect; the Supreme Court stayed implementation of the rule. Despite that, market forces resulted in the energy sector meeting the rule’s emissions reduction goals ahead of schedule, and EPA says it is working on new regulations.

The court nonetheless took up the case, saying in its opinion that the issues raised implicate the “major questions” doctrine.

“Under that doctrine’s terms, administrative agencies must be able to point to ‘clear congressional authorization’ when they claim the power to make decisions of vast ‘economic and political significance,’ Justice Neil Gorsuch said in a concurring opinion, quoting a previous Supreme Court decision. 

No such authorization exists in the Clean Air Act, the court found.

The majority opinion was written by Chief Justice John Roberts. He was joined by Gorsuch and Justices Samuel Alito, Clarence Thomas, Brett Kavanaugh and Amy Coney Barrett.

Justice Elena Kagan wrote a dissent in which she was joined by Justices Sonia Sotomayor and Stephen Breyer.

In it, Kagan wrote that the court’s decision “strips the [EPA] of the power Congress gave it to respond to ‘the most pressing environmental challenge of our time,’” citing the court’s 2007 decision in Massachusetts v. EPA, which held that EPA could regulate greenhouse gases such as carbon dioxide as “pollutants” under the CAA.

“The limits the majority now puts on EPA’s authority fly in the face of the statute Congress wrote,” Kagan said. “The majority says it is simply ‘not plausible’ that Congress enabled EPA to regulate power plants’ emissions through generation shifting. But that is just what Congress did when it broadly authorized EPA in Section 111 to select the ‘best system of emission reduction’ for power plants. The ‘best system’ full stop — no ifs, ands, or buts of any kind relevant here.”

The majority, however, looked at the same language in the CAA and had a different take.

“The government can offer only EPA’s authority to establish emissions caps at a level reflecting ‘the application of the best system of emission reduction . . . adequately demonstrated.’” The word ‘system’ shorn of all context, however, is an empty vessel. Such a vague statutory grant is not close to the sort of clear authorization required.”

The majority found it “'highly unlikely that Congress would leave'” to 'agency discretion' the decision of how much coal-based generation there should be over the coming decades," the majority said, quoting a previous decision.

Kagan, however, concluded her dissent by saying, “the court today prevents congressionally authorized agency action to curb power plants’ carbon dioxide emissions. The court appoints it­self — instead of Congress or the expert agency — the decision-maker on climate policy. I cannot think of many things more frightening.”

Reaction to the decision across the political spectrum was swift. 

National Rural Electric Cooperative Association CEO Jim Matheson said the ruling “clearly acknowledges that EPA overstepped its regulatory authority in the Clean Power Plan. The court’s decision resets the agency to its appropriate regulatory path, requiring it to set achievable emissions guidelines that can be accomplished at existing power plants while also allowing states to consider local factors and have the final say on compliance options.”

NRECA had joined with specific cooperatives to support the coal companies and 20 states that had brought the petition. 

Numerous environmental groups and climate scientists, as well as major power companies such as Con Ed, supported the Clean Power Plan, however.

“While the Supreme Court recognized EPA's authority to address pollution from existing fossil fuel power plants under the Clean Air Act, it constrains EPA’s authority to rely on clean energy solutions the power industry itself identified as the most common, proven and cost-effective,” the Environmental Defense Fund said.

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