On Tuesday, opposing sides took to the U.S. Court of Appeals for the District of Columbia Circuit to argue their cases on the merits of the Environmental Protection Agency’s landmark bid to control the emission of carbon dioxide, known as the Clean Power Plan. The U.S. Supreme Court issued a stay against the plan this past February, shortly before the passing of Justice Antonin Scalia.

The Appeals Court, the second most powerful court in the nation, for nearly seven hours on Tuesday heard arguments related to the plan, which would call for a reduction in carbon dioxide emissions from power plants by 32% from 2005 levels over the next 15 years. Sixteen lawyers represented the administration before the ten judges responsible for deciding the fate of the regulation. For their part, nearly two dozen states have joined with the power generation industry, coal mining companies, and the U.S. Chamber of Commerce to oppose the plan.

The last time the case came before the Appeals Court was in January, when the court, headed by Merrick Garland, later nominated to the Supreme Court by President Obama, refused to block the plan. According to at least one report, a final court decision on the Clean Power Plan may not come until as late as 2018. But with six of the ten judges having been named by Presidents Obama and Clinton, upholding the stay might be an uphill battle.

“This is a huge case,” remarked Judge Brett M. Kavanaugh, explaining that the new rule could “fundamentally” transform the industry. According to a report filed by CNN, Kavanaugh said the administration’s policy is “laudable” but questioned under the separation of powers whether Congress, and not the EPA, had to speak clearly on the issue of regulating carbon dioxide emissions.

Judge Thomas B. Griffith asked, “Why isn’t this debate going on in the floor of the Senate?” rather than before a panel of judges. But Judge Patricia A. Millet reiterated at one point that the Supreme Court “has already said” that the EPA has the authority to regulate in the area.

The questions raised by the judges strike at the heart of the debate over carbon dioxide regulation. Does EPA have the authority to unilaterally transform the energy industry?

The attitude of the judges toward the case appear to have been mixed. One Republican appointee, Thomas Griffith, said the new rule calls for only minor reductions in coal-fired plant emissions. Judge Kavanaugh, called the policy behind the plan “laudable,” adding, “The earth is warming, and humans are contributing.”

But according to CNN, “Kavanaugh also led the questioning of Justice Department lawyers making the case for EPA Administrator Gina McCarthy, who attended the morning session along with a phalanx of agency officials.”

“You’re setting unachievable limits in an effort to drive those (plants) out of business,” he told Justice Department lawyer Eric Hostetler. Unless Congress steps in, Kavanaugh said, “Lots of people are going to lose their jobs, lose their livelihoods.”

“We can’t tell a coal plant, ‘You have to become a solar plant,’” said Peter Keisler, a lawyer representing industry opponents. “EPA has no authority to impose a system like this one, which requires, in order to stay open, that the owner invests in other facilities.”

The appeals court has an important chance to set the record straight about the authority EPA has or doesn’t have. Let’s hope they carefully consider the merits of the case and make a conclusion that honors the law and benefits Americans.