Michigan vs. EPA, the Supreme Court continues to curtail EPA’s ability to regulate emissions from power plants by limiting the deference the Court will grant EPA on issues of statutory construction. In the 5 to 4 decision, authored by Justice Scalia and joined by Chief Justice Roberts and Justices Kennedy, Thomas, and Alito, the Court held that EPA’s air toxic standards for regulating mercury emissions from coal fired power plants were “unreasonable.” The Agency did not take into consideration the costs of regulation as a threshold matter before determining that regulation was “appropriate and necessary,” as required by the Clean Air Act. In reaching its conclusion, the Court cited to its recent decision inUARGto dramatically limit thedeference traditionally afforded executive agencies. The court stated: “(e)ven under this deferential standard, ‘agencies must operate within the bounds of reasonable interpretation.’” 576 U.S. _, 6 (2015).

The EPA regulation in question is the Mercury Air Toxic Standard (MATS). Before the Agency could promulgate MATS, Congress required that EPA perform a study to determine if mercury and other toxics still presented a threat to human health after reductions in those pollutants were achieved from other CAA programs, like the acid rain program. Congress laid out in the Clean Air Act that EPA could only impose these additional regulations on power plants if the Agency performed a study of the hazards to public health reasonably anticipated to occur as a result of emissions by power plants of hazardous air pollutants after imposition of the requirements of this chapter.” 42 U.S.C. §7412(n)(1)(A). If the Agency “finds . . . regulation is appropriate and necessary after considering the results of the study,” it “shall regulate [power plants] under [§7412].”Ibid.