In a 5-4 decision, the Supreme Court ruled the EPA was unreasonable when it did not consider costs when it decided to regulate mercury emissions from power plants. The Court, in an opinion by Justice Scalia, held that the EPA must consider costs, including compliance costs, when deciding whether a regulation is appropriate and necessary.

Yesterday, the Supreme Court heard oral arguments in Michigan v. EPA, a case that will decide whether the EPA properly decided to regulate mercury pollution from power plants. The problem with the regulations is that by the EPA’s own estimates they will cost $9.6 billion annually and have only $4-6 million in direct benefits. The issue before the Court will be whether the EPA must consider costs when deciding to regulate mercury emitted by power plants.