Why Delaware joined a lawsuit against the US Environmental Protection Agency

By Jay Shah

Published May 1, 2026 at 11:13 AM EDT

The US EPA under the Trump administration loosened federal standards regulating Mercury and other toxic emissions from coal and oil power plants in February 2026.

A group of 21 states and local governments filed a lawsuit against the United States Environmental Protection Agency, challenging its rollback of a Clean Air Act provision that regulates Mercury and other hazardous emissions from coal and oil-fueled power plants. Delaware joined that lawsuit, which was filed on March 31.

To help explain why this case matters and how it impacts the First State, Delaware Public Media’s Jay Shah spoke to Sarah Everhart - Assistant Professor and Director of the Environmental and Natural Resources Law Clinic at Widener University Delaware Law School.

Delaware Sues EPA

DPM's Jay Shah and Widener University Delaware Law School's Sarah Everhart discussed the significance of a lawsuit challenging the EPA's loosened Mercury and other toxic emission standards from coal- and oil-fired power plants.

Additional Notes:

The second lawsuit has been consolidated with the first petition filed by a group of environmental and public health groups, captioned Air Alliance Houston v. EPA, also filed in the U.S. Court of Appeals for the D.C. Circuit.

Delaware's initial filing in support of the Petition for Review of the Mercury and Air Toxic Standards (MATS) Rule was due on May 1, which would include a statement of the issues presented. This means they would present their initial basis for bringing forth the lawsuit. Then both sides have until May 18 to file their respective motions on this case. The EPA will most likely aim for a motion to dismiss the case and if granted, the petitioners including the First State, will file an appeal. Everhart said this motion can only be filed in the beginning of a case and the EPA will try to claim that the petitioners don't have grounds for a case.

She said the EPA will most likely claim that, "This case should not go forward because, for particular reasons. Like you don't have standing to bring it or the fact that this isn't like a case in controversy or this isn't something a court should be deciding because the court can't issue relief that would address the things that are at issue in the case."

However, if that dismissal isn't granted, then the lawsuit will move forward into the next round called "discovery" when the petitioners will have the opportunity to present detailed evidence to support their initial petition and statement of issues.