Mercury and Air Toxics Standards (MATS)

The Environmental & Energy Law Program is tracking the environmental regulatory rollbacks of the Trump administration. Click here for the list of rules we are following. If you’re a reporter and would like to speak with an expert on this rule please email us.

Why it Matters

MATS limits the amount of mercury and other toxic emissions from power plants. Mercury is a powerful neurotoxin that ends up in the water and soil, and concentrates up the food chain, especially in fish. It is particularly dangerous for pregnant women and young children. If the Environmental Protection Agency (EPA) were to reconsider or rescind the rule, power plants could stop operating the installed pollution controls.

Current Status

The Mercury and Air Toxics Standards were signed in December 2011, and coal- and oil-fired power plants required to make reductions to achieve those standards by the spring of 2016. Industry challenged the rule but the DC Circuit upheld the rule. The Supreme Court also left the rule intact — but sent one specific issue, the justification for doing the rule in the first place, back to the EPA to re-do. The Obama EPA completed the re-do on that issue, which industry then challenged. The Trump EPA has asked the DC Circuit to delay that case, saying “In light of the recent change in Administration, EPA requests continuance of the oral argument to give the appropriate officials adequate time to fully review the Supplemental Finding Litigation.” Litigation has been suspended indefinitely.


On February 16, 2012 EPA issued the final Mercury and Air Toxics Standards. Industry groups and several states challenged the rule. —Michigan v. EPA, No. 14-46 (lead case) (D.C. Cir.)

On June 29, 2015 the Supreme Court remanded MATS to EPA for additional cost-benefit analyses, to determine if the standards are “appropriate and necessary.”

EPA published its Supplemental Finding on April 25, 2016 on the costs and benefits of MATS. Within hours, opponents sued. –Murray Energy v. EPA, No. 16-1127 (D.C. Cir.)

Trump Era

On January 31, 2017 petitioners sought a 45-day extension in the briefing schedule. The D.C. Circuit denied the extension on February 9, 2017.

On April 18, 2017 EPA asked the Court to delay oral arguments, scheduled for May 18, 2017.

On April 27, 2017 the D.C. Circuit removed the argument from its calendar,  suspending the case indefinitely, and directed EPA to file 90-day status reports.

For More Information

For more on the history of this rule see its entry in the Columbia University Sabin Center for Climate Change Law’s database. Also see Sabin’s Climate Deregulation Tracker for additional updates.

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