On June 23, 2014, the U.S. Supreme Court issued a decision limiting U.S. EPA’s regulation of carbon emissions from stationary sources under the Greenhouse Gas (GHG) Tailoring Rule (Tailoring Rule). The Tailoring Rule phases the applicability criteria to determine which stationary sources become subject to GHG emission permitting requirements under PSD and Title V Clean Air Act programs (click here for more on the Tailoring Rule). While the Court upheld EPA’s authority to require sources, otherwise subject to PSD and Title V permitting due to their emissions of criteria pollutants, to comply with best available control technology for GHGs, the Court ruled that the Clean Air Act does not authorize EPA to require a source to obtain a PSD or title V permit solely on the basis of its potential GHG emissions.