Briefing before the U.S. Supreme Court is currently underway in a matter involving challenges to the suite of greenhouse gas (GHG) cases decided by the U.S. Court of Appeals for the District of Columbia Circuit in December 2012. In October 2013, the Supreme Court granted six petitions for writ of certiorari filed by industry and state petitioners on the following single issue:

Whether EPA [(the U.S. Environmental Protection Agency)] permissibly determined that its regulation of greenhouse gas emissions from new motor vehicles triggered permitting requirements under the Clean Air Act for stationary sources that emit greenhouse gases.