On Tuesday, February 9, 2016, the Supreme Court of the United States took the unprecedented step of halting the implementation of the Clean Power Plan while the plan is reviewed by a lower appeals court. The Clean Power Plan is a key platform of President Obama’s climate change action plan and would establish carbon pollution standards for existing power plants.

Fossil fuel-fired power plants are the largest source of CO2 emissions in the U.S. Although coal combustion represents about 39% of the electricity generated in the U.S., it accounts for 77% of CO2 emissions from the electricity sector. Under the Clean Power Plan, the Environmental Protection Agency (EPA) would require power plants to reduce carbon emissions by 32% by 2030.

Several states have brought a challenge against the Clean Power Plan to the U.S. Court of Appeal for the District of Columbia Circuit questioning whether the EPA has the legal authority to impose regulatory requirements on existing power plants. The Supreme Court, in issuing its order this week, did not decide on the substantive arguments in the challenges brought by the states. Rather, the Supreme Court considered only whether to stay the implementation of the requirements under the plan while the lower court considered the larger case brought by the states.

This delay in the implementation of the Clean Power Plan has caused some climate change policy experts to question whether the U.S. will be able to meet its commitment under the Paris Agreement to cut emissions 26 to 28% by 2025.

The U.S. Court of Appeal is scheduled to hear the legal challenge against the Clean Power Plan in June of this year.