The U.S. EPA has agreed to a request that it reconsider a rule that set federal limits on the levels of toxic metals that can be discharged from power plants.

The Effluent Limitations Guidelines and Standards rule, which was finalized in 2015, was the first to establish federal guidelines for the discharge of toxic metals like mercury, lead and selenium. At the time the rule was promulgated, more than 1,000 power plants in the United States were expected to begin complying with the rule between 2018 and 2023 as part of their renewal of Clean Water Act permits.

However, EPA Administrator Scott Pruitt recently agreed to stay the implementation of the rule after a group of more than 150 energy producers urged the EPA to reconsider it. Several companies had already filed legal challenges to the rule in court. The 5th Circuit Court of Appeals has agreed that those lawsuits should be held in abeyance pending the EPA’s reconsideration of the rule.

Administrator Pruitt offered a written explanation, stating that it was “in the public interest” to reconsider the timeframe for rolling out the rule. Pruitt indicated that he believed the timetable established by the Obama Administration for compliance with the new standards was not economically or technologically feasible. It was estimated to cost energy companies $1.2 billion per year during the first five years of compliance and $480 million per year thereafter.

Following the EPA’s announcement that it was staying the implementation of the rule, several environmental groups, including Clean Water Action and the Sierra Club, have filed their own lawsuit challenging the agency’s decision. The groups argue that the EPA failed to make the findings necessary to stay an administrative rule, including that legal challenges to the agency rule are likely to succeed on the merits and that irreparable harm would occur if a stay was not imposed. They argue the EPA’s decision was arbitrary and capricious.

The challenge to the EPA’s stay remains pending in Clean Water Action v. Pruitt, Number 1:17-cv-00817, in the U.S. District Court for the District of Columbia.