The US Supreme Court on Tuesday agreed to examine whether the Environmental Protection Agency exceeded its authority when it sought to regulate carbon dioxide and other greenhouse gases as pollutants under the Clean Air Act.

In a potential landmark case with substantial implications for the environmental health of the country as well as the health of the US economy, the high court said it would take up six of nine separate petitions filed with the court seeking review of the agency’s actions.

More than 70 business groups and public policy organizations, plus 13 states, filed petitions asking the high court to review various aspects of the EPA’s new regulations.

Some argued that the EPA’s broad reading of the Clean Air Act to allow the agency to enact and enforce a range of regulations of carbon dioxide usurped power reserved exclusively to Congress.

But the high court declined to hear petitions challenging the EPA’s so-called endangerment finding – that greenhouse gases pose a threat to public health and welfare. That finding triggered EPA authority to move forward with greenhouse gas regulations.

In denying three petitions but granting six others, the high court signaled that it will focus on issues further down the regulatory process.

Specifically, the court agreed to answer a single question: “Whether EPA permissibly determined that its regulation of greenhouse gas emissions from new motor vehicles triggered permitting requirements under the Clean Air Act for stationary sources that emit greenhouse gases,” the justices said in an order Tuesday.

Stationary sources include power plants, refineries, petrochemical plants, and heavy industry facilities.

Regulation of emissions of greenhouse gases is a high priority of the Obama administration.

Most environmental experts maintain that greenhouse gas emissions are contributing to global warming, including sea rise increases and more violent weather patterns. Other scientists say the data are unclear, and they question the connection between greenhouse gas emissions and fluctuations in atmospheric temperatures.

Industry groups have warned that EPA regulations would cost billions of dollars and hundreds of thousands of jobs, stalling the already-sluggish economic recovery. They say such profound policy decisions should be debated and approved by Congress rather than imposed by a regulatory agency.

Lawyers for the US Chamber of Commerce said in their brief the new regulations are “the costliest, farthest reaching, and most intrusive regulatory apparatus in the history of the American administrative state.”

The regulations, they said, could eventually “touch practically every aspect of every industry across the entire economy.”

A range of environmental groups and 17 states filed briefs supporting the EPA action and urging the Supreme Court to decline to hear any of the appeals.

Lawyers for the environmental groups argued in their briefs that the EPA’s regulation of stationary sources of greenhouse gases had gone well and that warnings about dire consequences for the nation are unfounded.

“No petitioner can credibly contend that the impact of greenhouse gas regulation as actually implemented is unreasonable or oppressive,” they said. “Permitting is proceeding at a reasonable pace across the country and across industrial sectors.”

In the first two years, they said, fewer than 200 large emitters – mostly electric power generators and natural gas processing plants – applied for permits. The process includes consideration of cost and is subject to judicial review, they said.

Critics of the EPA regulatory moves disagree. EPA officials, they argue, usurped the role of Congress to substantially expand the federal agency’s power to fight global warming.

The case went to the federal appeals court in Washington, D.C., which last year rejected industry complaints and upheld the EPA’s actions.

The three-judge panel cited a 2007 US Supreme Court decision, Massachusetts v. EPA, that held that greenhouse gases are a form of air pollution that could be covered by the Clean Air Act.

In the 5-to-4 decision, the high court said the agency had a duty to regulate greenhouse gases under the Clean Air Act if the EPA determined that greenhouse gases and related global warming pose a threat to public health and welfare.

The issue arose during the Bush administration, when the EPA refused to broaden enforcement of the Clean Air Act to include greenhouse gases.

In contrast, the EPA under President Obama has welcomed the opportunity to use the Clean Air Act to fight climate change. And the federal appeals court endorsed the Obama administration’s expansive application of the antipollution law.

“To be sure, the stakes here are high. The underlying policy questions and the outcome of this case are undoubtedly matters of exceptional importance,” the appeals court said.

The judges went on to note that the legal dispute involved a straightforward reading of the clean air statute and application of binding Supreme Court precedent to that statute.

Prior to appealing to the Supreme Court, lawyers for the industry groups asked the full appeals court to take up the case. It declined.

In a dissent from the appeals court decision not to rehear the case, Judge Brett Kavanaugh said regardless of how the case is decided, it would have “massive real-world consequences.”

Judge Kavanaugh said the EPA’s broad interpretation of “air pollutant” allowed it to expand the reach of federal regulation to include greenhouse gases. And that would expand the reach of the agency’s regulations.

But the expansion raised a problem within the statutory framework. Congress set thresholds for harmful pollutants that would require permits – 250 million tons per year for some facilities and 100 million tons for others.

The limits were set for six specifically identified pollutants – carbon monoxide, lead, nitrogen dioxide, ozone, particle pollution, and sulfur dioxide.

High concentrations of these pollutants in the air are considered capable of causing an immediate threat to human health. The Clean Air Act is aimed at addressing that threat.

In contrast, the threat from greenhouse gases is considered more remote. Greenhouse gases – such as carbon dioxide, methane, nitrous oxide, and hydrofluorocarbons – do not themselves pose an immediate threat to human health.

But the EPA is claiming broad regulatory power to address those wider threats to public welfare said to be posed by greenhouse gases and global warming.

In its endangerment finding, the EPA concluded that unprecedented levels of greenhouse gases pose a threat to public health and the welfare of current and future generations. Global warming, the agency concluded, would increase heat-related deaths and respiratory illnesses, boost the risks to health from violent hurricanes and other extreme weather events, and increase the prevalence of food and waterborne diseases.

Climate change could have adverse impacts on US food production, endanger forestry, increase the risk of extreme flooding and drought, increase the risk of storm surge and flooding related to sea level increases, and pose negative consequences for ecosystems and wildlife worldwide.

Critics of the EPA’s push to regulate greenhouse gases as if they are another variety of toxic pollutants argue that the problem is that greenhouse gases – like carbon dioxide and methane – are emitted in much larger quantities by a much larger universe of emitters.

Millions of industrial, residential, and commercial sources exceed existing regulatory levels.

If the original statutory thresholds for air pollution were applied to greenhouse gas emissions, the EPA would be unable to process all the permit applications. In addition to large industrial facilities, the new regulations could potentially also sweep in tens of thousands of lesser emitters including apartment buildings, large homes, schools, and hospitals, critics say.

Under established Clean Air Act thresholds, the number of permits would jump from 14,700 to 6.1 million. The new rules would require $22.5 billion in paperwork costs alone and additional billions in compliance costs, these critics say.

Recognizing this, the EPA rewrote the threshold for greenhouse gases. Rather than 250 tons, the agency set the limit at 100,000 tons. The action is unusual because the 250-ton restriction was written into the statute by Congress.

“This is a very strange way to interpret a statute,” Kavanaugh wrote in his dissent.

“When an agency is faced with two initially plausible readings of a statutory term, but it turns out that one reading would cause absurd results, I am aware of no precedent that suggests the agency can still choose the absurd reading and then start rewriting other perfectly clear portions of the statute to try to make it all work out.”

The judge added: “Allowing agencies to exercise that kind of statutory re-writing authority could significantly enhance the Executive Branch’s power at the expense of Congress’s and thereby alter the relative balance of powers in the administrative process.”

The Obama administration defends the EPA rules.

“Although it found some ‘uncertainties’ in the scientific data, the EPA determined that the body of scientific evidence compellingly supports the finding that greenhouse gases may reasonably be anticipated to endanger public health and public welfare by driving global climate change,” US Solicitor General Donald Verrilli wrote in his brief urging the court not to take up the case.

The appeals court decision, he said, was correct and reflected an accurate reading of the underlying statute and of the high court’s 2007 decision in the earlier Clean Air Act case.