U.S. EPA's cornerstone Mercury and Air Toxics Standards (MATS) were back in court this week. After being upheld by the U.S. Court of Appeals for the District of Columbia Circuit last year, oral arguments were heard by the Supreme Court yesterday. The question before the court is whether EPA should have considered costs before moving forward with its MATS rule. During today's OnPoint, Richard Revesz, director of the Institute for Policy Integrity at New York University School of Law, assesses the arguments presented and questioning by the justices. He also comments on Harvard Law School professor Laurence Tribe's constitutional arguments against EPA's Clean Power Plan. Today's OnPoint will air on E&ETV at 10 a.m. EDT.