On July 8, 2019 US EPA published its rule to replace the 2015 Clean Power Plan, the Affordable Clean Energy (ACE) rule. The 2015 Clean Power Plan was issued as part of EPA’s court-mandated requirement to regulate greenhouse gases from power plants under the Clean Air Act. However, following considerable litigation and opposition from the Trump administration, EPA announced in 2017 that it would repeal and replace the plan. The ACE rule will not establish emissions caps, but will instead give states broad flexibility in determining how stringently they want to control power plant emissions under their jurisdiction. The rule will also make less strict the efficiency threshold for when New Source Review applies to facilities. The rule will also extend the timeline for when states must submit their plans to more closely match the schedule required for state implementation plans under the National Ambient Air Quality Standards. The rule becomes effective on September 6, 2019.