In what is being hailed as a major victory for public health, the U.S. Supreme Court on Tuesday affirmed the Environmental Protection Agency's authority to regulate cross-state air emissions from polluting factories and power plants.

In a 6-2 decision, the Court upheld the Cross-State Air Pollution Rule, commonly known as the Transport Rule, which required 28 eastern states to reduce power-plant emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx), which often form smog and worsens air quality across state lines.

"Air pollution is transient, heedless of state boundaries," wrote Justice Ruth Bader Ginsberg, who delivered the opinion for the Court. "Left unregulated, the emitting or upwind State reaps the benefits of the economic activity causing the pollution without bearing all the costs."

After being adopted by the EPA in 2011, power companies and several states sued to block the rule from taking effect and in 2012 a federal court ruled to invalidate the rule.

"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," said John Walke, director of the Clean Air Program at the Natural Resources Defense Council, in a statement following the ruling. "The Supreme Court wisely upheld this common-sense approach."

Walke added that these "long-overdue protections" will save "tens of billions of dollars a year in health costs" and defend the health and safety of millions who live downwind from polluting power plants.

"For too long, these communities have shouldered an unfair burden on their health and well-being without the ability to protect themselves and their families from dangerous pollution," added Michael Brune, executive director of the Sierra Club.

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