On April 30, 2018, the Environmental Protection Agency (EPA) provided notice of proposed rulemaking (83 FR 18768) intended to strengthen the transparency of EPA regulatory science. On March 18, 2020, EPA issued a supplemental proposal (SNPRM) to clarify, modify and supplement certain provisions of the 2018 proposed rule in response to public comments. In the SNPRM, EPA proposed definitions and clarified that the proposed rulemaking applies to data and models underlying both pivotal science and pivotal regulatory science. EPA also proposed that the scope of the rulemaking apply to influential scientific information as well as significant regulatory decisions and proposed a modified approach to the public availability provisions for data and models that would underlie significant regulatory decisions and an alternate approach. Finally, EPA requested comment on whether to use its housekeeping authority independently or in conjunction with appropriate environmental statutory provisions as authority for taking this action. This action would increase transparency of the assumptions underlying data and models that support these EPA regulatory decisions.