In some references, the surname of West Virginia’s attorney general was misspelled in an earlier version of this article. Patrick Morrisey, not Morrissey, is his name.

The Supreme Court will hear arguments in the most important environmental case in more than a decade on Monday, in a dispute that could limit or even eliminate the Environmental Protection Agency’s authority to control the pollution that is heating the planet.

A decision by the Supreme Court, which has a conservative supermajority, could jeopardize President Biden’s plans to cut greenhouse gas emissions in half by the end of the decade, which scientists say is required to avoid the most catastrophic effects of climate change. However, the outcome could have far-reaching consequences beyond air pollution, limiting federal agencies’ ability to regulate health care, workplace safety, telecommunications, the financial sector, and other areas.

The issue is a federal regulation that governs power plant emissions in general. However, in an unusual twist, the regulation never went into effect and no longer exists.

The legal wrangling began in 2015, when President Barack Obama announced the Clean Power Plan, his primary climate change strategy. The Obama administration planned to use its authority under the Clean Air Act to require each state to reduce carbon dioxide emissions from the electricity sector, primarily by replacing coal-fired power plants with wind, solar, and other clean sources. After transportation, electricity generation is the second largest source of greenhouse gas emissions in the United States.

The Clean Power Plan, however, was never implemented. Following a slew of lawsuits from Republican states and the coal industry, the Supreme Court halted the program. When President Donald J. Trump took office, he implemented a new plan that effectively amounted to no regulation. However, on the last full day of Mr. Trump’s presidency, a federal appeals court ruled that the Trump administration had “misconceived the law,” and the Trump plan was thrown out. This paved the way for the Biden administration to issue its own rule, which it has yet to do.

According to legal experts, it is extremely unusual for the Supreme Court to hear a case involving a hypothetical future regulation.

The plaintiffs in the case, West Virginia v. Environmental Protection Agency, want the Supreme Court to prevent the kind of sweeping changes to the electricity sector that characterized Obama’s Clean Power Plan.

Instead, Republican attorneys general in 18 states and some of the nation’s largest coal companies will argue that the 1970 Clean Air Act limits the E.P.A.’s authority to impose changes only at individual power plants, rather than across the entire power sector.

Conservatives have long argued that the executive branch routinely exceeds its constitutionally granted authority in regulating all types of economic activity. Others argue that under the Clean Air Act, Congress delegated authority to the executive branch to broadly regulate air pollution. They claim that the legislature creates the law and that the executive implements it through regulation.

With the stakes so high, each side has gathered legal support from a diverse group of supporters. Many of the country’s largest electric utilities — the companies that would be subject to environmental regulation — have filed legal briefs in support of the government. They are joined by 192 members of Congress, the United States Conference of Mayors, climate and public health advocates, and tech behemoths such as Apple, Google, and Netflix.

91 members of Congress and some of the nation’s most powerful conservative groups, including Americans for Prosperity Foundation, a group affiliated with the libertarian Koch family and their billions, are supporting the plaintiffs.

Mr. Morrisey said he was encouraged by the court’s 6-3 split between conservatives and liberals, which included three Trump appointees. “We’re optimistic about the outcome,” he said.

Mr. Morrisey’s optimism is probably well-founded, according to Biden administration officials and environmentalists, given both the composition of the court and recent decisions against federal rules, such as blocking a federal vaccine mandate and ending Mr. Biden’s eviction moratorium.