On June 26, 2012, the U.S. Court of Appeals–D.C. Circuit upheld EPA's Endangerment Findings and greenhouse gas regulations issued under the Clean Air Act for passenger vehicles and Clean Air Act permitting for stationary sources.

In 2007, the Supreme Court ruled in Massachusetts v. EPA that greenhouse gases are covered by the Clean Air Act's definition of air pollutant and that EPA must determine whether or not emissions of greenhouse gases from new motor vehicles cause or contribute to air pollution that may reasonably be anticipated to endanger public health or welfare.

EPA was challenged through a group of lawsuits over its actions resulting from the Supreme Court decision to address greenhouse gases, including:

1. The 2009 Endangerment Findings, in which EPA determined that greenhouse gases endanger the health and welfare of Americans.
2. The Light-Duty Vehicle Rule, in which EPA coordinated with the National Highway Traffic Safety Administration to develop harmonized regulations to reduce greenhouse gas emissions and improve the fuel economy of light-duty vehicles.
3. The Tailoring Rule, in which EPA set greenhouse gas emission thresholds to define when permits under the New Source Review Prevention of Significant Deterioration (PSD) and Title V Operating Permit programs are required for new and existing industrial facilities.

See the 2012 Court of Appeals–D.C. Circuit Decision on Endangerment.

The U.S. Chamber of Commerce and the National Association of Manufacturers (with others) filed petitions to the U.S. Court of Appeals–D.C. Circuit to rehear the case. The Department of Justice and EPA provided a response on Friday, October 12, 2012.

See the petitions and EPA's response.