The Supreme Court curbed the EPA's ability to regulate mercury emissions from power plants on Monday by a 5–4 vote. In an opinion by Justice Antonin Scalia, the court held that the EPA did not properly take into account the cost to plants complying with the new standards. The EPA had argued that it did not need to consider these costs until later in the regulatory process. Scalia, joined by his fellow conservatives, holds that the EPA's refusal to consider these costs when creating the mercury regulations was unreasonable.
This ruling does not invalidate the mercury regulations altogether. Rather, it simply requires the EPA to reconsider costs to power plants before deciding whether the regulations are "appropriate and necessary." Presuming it considers these costs and decides that the regulations remain necessary, the EPA may again impose the new emissions standards.