This action proposes changes to the National Emission Standards for Hazardous Air Pollutants for Coal- and Oil-Fired Electric Utility Steam Generating Units (commonly referred to as the Mercury and Air Toxics Standards (MATS)), 40 CFR 63, subpart UUUUU, that would provide clarity and flexibility with regard to some monitoring, recordkeeping, and reporting provisions in the final rule, initially promulgated on February 16, 2012 (77 FR 9304), and most recently amended on April 6, 2016 (81 FR 20172). In an April 2017 court filing, EPA requested that oral argument for MATS litigation be continued to allow the current Administration adequate time to review issues raised in petitions for reconsideration. This action addresses the review of those issues, as well as suggests revisions necessary to merge separate electronic reporting systems into one system.