The Supreme Court has rejected an appeal from 20 states seeking to block a federal rule targeting mercury pollution from taking effect while the government revises the rule to account for compliance costs.

The justices on Monday left in place a federal appeals court ruling that said the rule could remain in place while the Environmental Protection Agency fixes legal problems and comes out with a revision. The EPA revised its cost analysis in April.

The high court ruled last year that the EPA should have considered costs and benefits before imposing limits on mercury and other air pollutants from coal- and oil-fired power plants. But the justices let the rule stay in effect while the lower court decided how a cost-benefits analysis should be conducted.