(CNN) -- A key part of the Obama administration's green policies received surprisingly strong Supreme Court support on Tuesday over efforts to curb air pollution.
A 6-2 majority of justices issued a decision upholding federal agency rules to control coal-fired power plant emissions from 28 states.
It was a rare environmental victory in a conservative majority court that has in recent years generally sided against the federal government's nationwide clean air policies.
The issue was complex -- whether an "upwind" state that is polluting a "downwind" state is free of any obligations under the so-called Good Neighbor provision, unless and until federal regulators have quantified the upwind state's contribution to downwind state's air pollution problems.
The case was an important test of federal regulatory power, and the rules issued two years ago by the Environmental Protection Agency were challenged by a coalition of 15 states, as well as several energy companies and labor unions.
Leaders in some mostly conservative states say lost jobs and higher energy costs are at stake from what they see as arbitrary and ambiguously enforced regulations.
But the administration and its environmental allies counter Americans' health should come first, and that as many as 45,000 deaths could be prevented each year if the Cross-State Pollution Rule would be allowed to take effect.
The high court agreed to a large extent.
"The Good Neighbor Provision, in our view, entrusts interpretive authority to EPA," said Justice Ruth Bader Ginsburg. "We are satisfied that EPA's construction of the statute reasonably responded to a perplexing problem the statute itself does not resolve."
Shortly before the court's December arguments, a coalition of eight of nine governors from the affected downwind states signed a petition urging the EPA to force nine southern and midwestern upwind states to reduce smog and soot emissions from power plants.
The one downwind governor who did not sign was New Jersey's Chris Christie.
Those Democratic or Independent governors criticized an earlier federal appeals court ruling against federal oversight, saying it "allows upwind states to postpone the costs of air pollution controls for years, while in the interim downwind states and their residents are forced to suffer the present consequences of that pollution."
Enforcement of what is known as the Transport Rule was adopted by the EPA in 2011, but remained on hold while the court cases worked toward conclusion. The agency should soon be allowed to put the revised regulations in place.
The Justice Department had urged the court to allow the EPA to use the somewhat discretionary standard "contribute significantly," when determining a state's cost-based share of transported air pollution.
In a typically thunderous dissent, Justice Antonin Scalia said, "Today's opinion is a textbook example of how a court established to assure government by the people can instead assure government by the bureaucracy."
He said the majority's reasoning will only encourage "rogue administration of the law."
Scalia made his comments from the bench, an unusual tactic for a dissent. He was supported by Justice Clarence Thomas. Justice Samuel Alito did not take part in the cases.
Among the provisions being challenged was the EPA's cost-based formula, using what it calls a balance between an upwind state's obligation to reduce coal-fired pollution, and the amount of money that would be required for a downwind state to feasibly meet its own obligations.
That calculation was a key part of the decision's calculus, which critics of the policies say unfairly punishes some states more than others, by placing a greater financial burden for their share of unhealthy air particulates.
Texas Solicitor General Jonathan Mitchell had told the court, "EPA's actions in this case have written the states out of the Clean Air Act. EPA has left the states completely in the dark about the meaning of the phrase 'contribute significantly.'"
The justices have yet to issue a ruling in another related and closely watched environmental case: can the EPA tighten emission standards for "stationary" greenhouse gas sources -- such as power plants -- in what the government says is an effort to stem the effects of global warming.
The high court in 2007 affirmed the conclusions by much of the scientific community that greenhouse gases are an air pollutant, but that case just dealt with emissions from motor vehicles. The high court will decide if the agency properly extended its regulatory authority.
The consolidated cases decided Tuesday are EPA v. EME Homer City Generation (12-1182) and American Lung Assn. v. EME Homer City Generation (12-1183).