In Sierra Club v. EPA, the Third Circuit Court of Appeal held that the Environmental Protection Agency’s (EPA) approval of Pennsylvania’s State Implementation Plan (SIP) was arbitrary and capricious because it failed to lower emissions, had a broad exception, and gave operators wide reporting discretion. The court held that these elements, taken together, demonstrated that agency approval was inappropriate. This In Brief argues that EPA should never have approved the Pennsylvania SIP because the operators’ reporting discretion component demonstrated that the proposed limitations did not comply with the Clean Air Act (CAA). The plan did not comply with the CAA and lacked an enforcement mechanism because it gave wide reporting discretion to operators. Here, undue reporting discretion refers to allowing operators to self-report exceedance of temperature thresholds without imposing strict data requirements as well as using vague EPA standards for when to report. As such, operators can choose what to report, giving EPA no way of ascertaining if a standard has been violated. Thus, EPA should reject a SIP when operators have undue reporting discretion because it makes regulation essentially unenforceable. Here, the court’s reliance on the three characteristics taken together rather than just the undue reporting discretion and resulting unenforceability undermines the CAA.