On February 16, 2012, EPA promulgated National Emission Standards for Hazardous Air Pollutants for Coal- and Oil-fired Electric Utility Steam Generating Units (77 FR 9304). The rule (40 CFR part 63, subpart UUUUU), commonly referred to as the Mercury and Air Toxics Standards (MATS), includes standards to control hazardous air pollutant emissions from new and existing coal- and oil-fired electric utility steam generating units located at both major and area sources of hazardous air pollutant emissions. There have been several regulatory actions regarding MATS since February 2012, including a May 22, 2020, action that completed a reconsideration of the appropriate and necessary finding for MATS and finalized the residual risk and technology review conducted for the Coal- and Oil-Fired Electric Utility Steam Generating Unit source category regulated under MATS. The Biden Administration's Executive Order (EO) 13990, Protecting Public Health and the Environment and Restoring Science To Tackle the Climate Crisis, "directs all executive departments and agencies (agencies) to immediately review and, as appropriate and consistent with applicable law, take action to address the promulgation of Federal regulations and other actions during the last 4 years that conflict with these important national objectives, and to immediately commence work to confront the climate crisis." On January 20, 2021, the Biden-Harris Transition released a preliminary list of actions that should be reviewed in accordance with EO 13990. On the list of EPA actions is "National Emission Standards for Hazardous Air Pollutants: Coal- and Oil-Fired Electric Utility Steam Generating Units-Reconsideration of Supplemental Finding and Residual Risk and Technology Review," 85 Fed. Reg. 31286 (May 22, 2020). As directed by EO 13990, EPA will review the May 22, 2020 final action and, under this action, will take appropriate action resulting from that review.