In December 2018, an article in this blog flagged a petition for EPA rulemaking under the Toxic Substances Control Act (TSCA) that, if denied, had the potential to set up precedent-setting litigation on citizens’ ability to use the courts to require EPA action under TSCA. Now, nearly a year later, the scenario that article described is coming true. In a challenge to EPA’s denial of that petition, a federal district court is poised to decide what constitutes a petition for issuance of a new rule as opposed to one for amendment of an existing rule—and in the process, to decide when a court may cast aside deference to EPA and undertake its own evaluation independent of the Agency’s record and conclusions.