The attorneys general (AGs) of 20 states have asked the U.S. Supreme Court to stay EPA’s Mercury and Air Toxics Standards (MATS) because the Agency had no legal authority to promulgate them. The AGs base their argument on the Supreme Court’s ruling in Michigan v. EPA (2015), in which a 5–4 majority ruled that the Agency had acted unreasonably by not taking cost into consideration in the MATS rulemaking.
Without vacating MATS, the majority remanded the case to the U.S. Court of Appeals for the D.C. Circuit, which then agreed with EPA’s request to leave MATS in place. But according to the AGs, by not fulfilling the “precondition” of cost consideration, the Agency never obtained the authority to issue MATS in the first place, and until that precondition is met, electric power plants are being forced to comply with unlawful requirements.