Dive Brief:

• Leaders from 20 states filed a brief Tuesday with the Supreme Court asking it to block the Obama administration from enforcing the Mercury and Air Toxics Standards (MATS), a set of air quality rules aimed at reducing emissions of harmful pollutants from power plants. 
• Last year, the Supreme Court rejected the MATS rule, saying the agency should have done a cost-benefit calculation before beginning to write the regulation. The decision tossed the rule back to the D.C. Circuit Court, which ruled in December that the EPA could continue enfocing the rules while assessing how to fix the regulatory package.
• Most of the coal power plants affected by the MATS rule have either made the necessary emission control upgrades or have shut down. About 200 plants, however, were granted extensions to the original compliance deadline in April 2015 and will still need to meet the regulatory standards if the rule stands.

Dive Insight:

While the Supreme Court rejected the MATS plan in June 2015, it did so on such narrow grounds that the EPA is still enforcing the rules. 

The ruling, Utility Dive reported at the time, centered on how the agency determined that the rules were "appropriate and necessary," an initial finding that begins the process of writing a regulation. The plaintiffs argued the agency should have considered the costs of the eventual regulation at that point. The EPA argued that it factored cost into the regulatory process at multiple points and that it was under no specific obligation from the Clean Air Act to factor them in for that initial finding. 

The Supreme Court, in an opinion penned by the late Justice Antonin Scalia, sided with the plaintiffs, writing that the agency should have factored in costs at the beginning. But the ruling did not question the EPA's ability to regulate mercury and other air toxins. Instead, it kicked the rule back down to the D.C. Circuit Court, which was tasked with deciding how the EPA should proceed. 

In December, the D.C. Circuit ruled that the agency could continue to enforce the MATS rule as it fixed the flaws in the program identified by the Supreme Court. Obama administration lawyers told The Hill the fix would be completed by April 16. 

While a Supreme Court block on a rule it has already considered would be unusual, critics of the MATS rules may feel emboldened by a recent unexpected ruling on another Clean Air Act regulation — the Clean Power Plan. Earlier this month, the court sent shockwaves through the power sector when it placed a judicial stay on the plan, preventing any enforcement of the carbon standards until all court proceedings are complete. 

The motivation behind that stay may have come in part from the enforcement situation involving MATS. When the Supreme Court heard hearings on the rule last year, the MATS compliance period had already begun and most plants affected by the regulations had either made the necessary upgrades to control emissions or had already shut down. 

About 200 plants — representing roughly 20% of U.S. generating capacity — were granted one-year extensions to the April 2015 under the rule. If the rule were vacated completely, regulatory lawyers told Utility Dive in June, utilities that had already made billion-dollar investments in pollution control equipment to meet the extended compliance deadline could have to face prudence reviews from state regulators on the expenditures. 

No matter how the Supreme Court rules, the MATS rules have already meant major consequences for the nation's generators. In late 2015, the Sierra Club released estimates that more than 20 GW of coal-fired generation would come offline before the end of the year, largely due to the MATS rule, other EPA air regulations and the low price of natural gas: