The U.S. Court of Appeals for the District of Columbia invalidated a pair of EPA rules in February that would have allowed coal-fired power plants a reprieve on complying with new federal mercury regulations.

The court found a provision in the 2005 rule to remove power plants from the Clean Air Act’s list of toxic sources – replacing it with a cap and trade regulatory scheme – to be in violation of the act. Greenhouse gases and global climate change are now urgent business issues.

The Clean Air Mercury Rule (CAMR) was set to go into effect in 2010. Power plants that failed to meet emission targets, under the rule, would have been allowed to buy credits from plants that did, rather than having to install their own mercury emissions controls.

Although many states created their own mercury controls, CAMR was the first nation-wide control rule, which was a primary arguing point for the agency during the trial.

The plan to exempt coal and gas power plants immediately came under fire from environmental organizations. Fourteen states and a number of Native American tribes joined these organizations in the suit. According the Waterkeeper Alliance, one of the groups who joined the suit, the agency will now be obligated to develop maximum achievable control technologies, or MACT, standards for power plant mercury emissions.

The three-judge panel unanimously agreed with the states that the EPA did not have the authority to exempt the power plants.