The Environmental Protection Agency acted consistently with the requirements of the Clean Air Act when it promulgated new regulations to control air pollution drifting from power plants across state lines, the US Supreme Court ruled on Tuesday.

In a 6-to-2 decision, the high court endorsed the EPA’s Cross-State Air Pollution Rule that seeks to limit power-plant emissions in 28 upwind Eastern and Midwestern states to help reduce air pollution levels in downwind states. The action falls under the so-called Good Neighbor Provision of the Clean Air Act.

“EPA’s cost-effective allocation of emissions reductions among upwind states, we hold, is a permissible, workable, and equitable interpretation of the Good Neighbor Provision,” Justice Ruth Bader Ginsburg wrote in the majority opinion.

In a dissent, Justices Antonin Scalia and Clarence Thomas criticized the majority justices for allowing the EPA to exceed limits on the agency’s authority that they said are written into the Clean Air Act.

“Today’s decision feeds the uncontrolled growth of the administrative state at the expense of government by the people,” Justice Scalia said in a statement from the bench. The result of the EPA’s action may be a more efficient regulation of cross-state pollution, he said, but “it comes at the expense of endorsing, and thereby encouraging for the future, rogue administration of the law.”

Environmental groups praised the ruling, while critics of the EPA’s regulatory approach said it marked an expansion of federal power.

“Today’s Supreme Court decision is a resounding victory for public health and a key component of EPA’s efforts to make sure all Americans have clean air to breathe,” EPA Administrator Gina McCarthy said in a statement.

The EPA has estimated that its new regulations will help prevent as many as 34,000 premature deaths a year from air pollution.

Under the rules, the agency sought to control emissions of sulfur dioxide and nitrogen oxides that are swept through the air to neighboring states. The airborne pollutants complicate efforts in downwind states to maintain acceptable levels of air quality.

The dispute in the case was over how the EPA went about determining how much a contributing state must reduce emissions. The agency set limits based on the cost of power plants' prior antipollution investments in a given state, rather than focusing strictly on the amount of pollution being released.

Fourteen states and various industry groups opposed the new regulations and challenged them in court. They argued that there is no relationship between how much a state contributed to a downwind pollution problem and how much the government would require it to reduce emissions.

Under the EPA's new system, some states that contribute less to the problem would nonetheless be required to take expensive steps to reduce emissions by more than other states.

A federal appeals court in Washington invalided the new regulations in 2012. It ruled that the EPA’s rules did not give states a meaningful opportunity to adopt their own plans to comply with federal pollution targets. The Good Neighbor Provision was written to foster a state-federal partnership in attacking air pollution, not to create a top-down federally imposed mandate, the appeals court said.

The appeals court also objected to the EPA’s decision to rely on a cost-benefit analysis to determine each state’s obligation in solving the cross-state pollution problem. The appeals court said the Clean Air Act authorizes the agency to regulate based only on the amount of pollutants contributed by each state.

Reversing the federal appeals court, the Supreme Court said the EPA did not have to defer to each state before imposing a national standard to limit cross-state pollution.

“In rejecting EPA’s reading of the substance of the Good Neighbor Provision, the [appeals court] failed to give the agency’s interpretation due respect,” Justice Ginsburg said in a statement from the bench.

She added that the EPA acted within its authority in writing a regulation that relies on cost-benefit analysis rather than limiting its approach to the amount of pollution each state emits.

“We read Congress to have delegated to the agency authority to choose among reasonable options,” Ginsburg said. She said the EPA’s decision to embrace a cost-benefit approach aims to achieve “an impressively lower overall cost.”

Joining Ginsburg in the majority were Chief Justice John Roberts and Justices Anthony Kennedy, Stephen Breyer, Sonia Sotomayor, and Elena Kagan.

Justice Samuel Alito did not participate in the case.

In his dissent, Scalia said the majority opinion affords greater power to federal regulators. “Too many important decisions of the federal government are made nowadays by unelected agency officials exercising broad lawmaking authority, rather than by the people’s representatives in Congress,” he wrote.

Scalia said Congress was specific in requiring the EPA to regulate the amounts of pollutants, not the cost of pollutants. The high court decision, he said, endorses “an undemocratic revision of the Clean Air Act.”

Scalia added that the decision ignores the state-federal balance Congress sought to maintain by requiring cooperation, not federal dominance, in the regulation of pollution.

“The EPA usurped the authority of not just Congress, but also the states,” he said. “The Clean Air Act rests on a foundation of cooperative federalism: EPA sets air-quality benchmarks for states, and the states then select their chosen means of achieving those benchmarks.”

He said EPA can intercede only if the state does not effectively address the problem. “But here, in order to set up the cap-and-trade markets it so desperately desired, EPA promulgated federal implementation plans … without giving the states a chance to come up with their own strategies for hitting those newly announced targets,” Scalia said.

In reaction to Tuesday's decision, Richard Faulk, senior director of the Energy and Environment Initiative at George Mason University, said the majority justices had ignored the Clean Air Act’s reliance on state-federal partnership.

“Although the Clean Air Act plainly requires ‘cooperative federalism’ – the Supreme Court majority has refused to allow the states to have any voice in the practicalities of determining the impact of their emissions on neighboring states,” Mr. Faulk said in a statement.

“Cooperative federalism requires more than a nod and a wink – it requires true collaboration,” he said.

Environmental groups praised the decision as an important advance for the environment and public health.

“Today’s Supreme Court decision means that millions of Americans can breathe easier,” Fred Krupp, president of the Environmental Defense Fund, said in a statement.

John Walke of the Natural Resources Defense Council said the decision will let the EPA move forward with a new regulatory regime that will help save lives and cleanse the air.

“The EPA safeguards follow the simple principle that giant utility companies shouldn’t be allowed to dump their dirty emissions onto residents of downwind states,” he said. “The Supreme Court wisely upheld this common-sense approach.”