The Supreme Court has ruled against federal regulators' attempt to limit power plant emissions of mercury and other hazardous air pollutants.
The rules began to take effect in April, but the court said by a 5-4 vote Monday that the Environmental Protection Agency failed to take their cost into account when the agency first decided to regulate the toxic emissions from coal- and oil-fired plants.
The challenge was brought by industry groups and 21 Republican-led states.
Writing for the court, Justice Antonin Scalia said it is not appropriate to impose billions of dollars of economic costs in return for a few dollars in health or environmental benefits.
The case now goes back to lower courts for the EPA to decide how to account for costs.