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The U.S. Supreme Court remanded the Mercury and Air Toxics Standards or "MATS" rule to the DC Circuit Court after finding that the EPA had not properly considered cost as part of the "Appropriate and Necessary" Finding that was required under Clean Air Act section 112(n)(1)(A). On December 15, 2015, the DC Circuit Court remanded the rule back to the EPA (without vacatur) to allow the Agency to correct the deficiency identified by the Supreme Court. A proposed rule was published in the Federal Register on December 1, 2015. The EPA will issue a final supplemental finding that details how the Agency explicitly considered cost and that such consideration of cost does not alter the EPA's previous determination that it is appropriate to regulate hazardous air pollutant emissions from coal- and oil-fired electric utility steam generating units.