The U.S. Supreme Court on Monday began hearing arguments in a case that could curb the use of federal power to address environmental issues and undermine President Joe Biden's plan to tackle climate change.

The court, whose 6-3 conservative majority has shown wariness toward broad federal agency actions, was weighing the Environmental Protection Agency's (EPA) authority to regulate greenhouse gas emissions from existing coal- and gas-fired power plants under the landmark Clean Air Act.

An eventual ruling restricting the EPA's authority could hamstring the administration's ability to curb the power sector's emissions - representing about a quarter of U.S. greenhouse gases. The United States, behind only China in greenhouse gas emissions, is a pivotal player in efforts to combat climate change on a global basis.

The Supreme Court will review the U.S. Court of Appeals for the District of Columbia Circuit's 2021 decision striking down Republican former President Donald Trump's Affordable Clean Energy rule. That regulation would have imposed limits on a Clean Air Act provision called Section 111 that provides the EPA authority to regulate emissions from existing power plants.

The argument was held hours after the release of a 3,675-page United Nations report urging action on a global scale to combat climate change. Outside the Supreme Court, a small group of demonstrators carried signs reading "Protect the Clean Air Act."

The case was pursued by Republican-led states led by coal producer West Virginia. Other challengers include coal companies and coal-friendly industry groups. Coal is among the most greenhouse gas-intensive fuels.

Democratic-led states and major power companies including Consolidated Edison Inc, Exelon Corp and PG&E Corp sided with Biden's administration, as did the Edison Electric Institute, an investor-owned utility trade group.

The rule proposed by Trump, a supporter of the U.S. coal industry who also questioned climate change science, was meant to supplant Democratic former President Barack Obama's Clean Power Plan mandating major reductions in carbon emissions from the power industry.

The Supreme Court blocked implementation of the Clean Power Plan in 2016 without ruling on its lawfulness.

Coal-aligned groups now want the justices to rule that Biden's administration cannot take a sweeping approach to regulating carbon emissions under Section 111. Such a decision would prevent the EPA from enforcing industry-wide changes, limiting it to actions targeting individual plants.

That would be a blow for Biden's administration, which has a goal of decarbonizing the U.S. power sector by 2035. The White House's incentive-based proposal to achieve that goal was rejected in Congress during budget and infrastructure legislation negotiations.

The Supreme Court already has shown antagonism toward broad agency actions, most recently on Jan. 13 by blocking Biden's COVID-19 vaccine-or-test mandate for large employers.

The court previously has cited what is called the "major questions" doctrine in blocking other government agency actions.

The court potentially could dismiss the appeal if the justices conclude the challengers lack proper legal standing with no regulation currently on the books.

If Biden's administration loses the case, Congress would need to pass new legislation for the government to impose sweeping climate-related regulations - an unlikely prospect in the near-term given stubborn divisions among lawmakers.

A ruling is expected by the end of June.