The Supreme Court agreed Friday to hear a set of cases challenging the Environmental Protection Agency’s authority to regulate greenhouse gases, potentially limiting the Biden administration’s options to curb planet-heating pollution.

The lawsuits, filed by Republican-controlled states and a West Virginia oil company, aim to curb the federal government’s power to mandate a transition away from fossil-fueled power plants.

If the high court’s 6-3 conservative majority finds in favor of the plaintiffs, the ruling wouldn’t eliminate the federal government’s ability to regulate carbon dioxide emissions under the Clean Air Act, a legal determination known as the endangerment finding. It would, however, restrict the legal routes through the Clean Air Act for enacting such rules. That could make it harder for the United States to hit its goal to cut emissions in half by the end of this decade.

In an updated grant of certiorari, the Supreme Court said it plans to ask questions about a legal issue known as “non-delegation doctrine,” which Cornell Law School describes as the “principle in administrative law that Congress cannot delegate its legislative powers to other entities.”

A ruling that explicitly requires Congress to pass new laws allowing EPA to regulate carbon emissions could prove an even bigger setback.

The White House abandoned its main legislative proposal to pay utilities to produce more zero-carbon electricity, and fine those that fail to increase their clean output each year, after Sen. Joe Manchin (D-W.Va.) said he’d torpedo the administration’s agenda if Democrats included the measure in a sweeping spending bill currently under consideration. Democrats are also expected to lose control of Congress in next year’s election.