In a shift of federal policy with potentially sweeping implications for civil enforcement, the U.S. Department of Justice (DOJ) recently announced it will no longer rely on guidance documents as the basis for bringing enforcement actions. The DOJ, rather than the agencies themselves, oversees and prosecutes a host of government cases that meet certain penalty thresholds. The new policy is particularly significant for environmental enforcement actions, which often reference requirements laid out in agency guidance, as opposed to formally promulgated regulations and statutes. Agency guidance is not subject to formal rulemaking procedures, however, and as a result cannot create legally binding requirements. When regulations and statutes are ambiguous or vague, the government often invokes agency guidance for clarification, specificity, and detail. The Environmental Protection Agency (EPA), for example, utilizes guidance documents to guide private party remediation efforts at Superfund sites and to effectuate the enforcement of Superfund settlements and unilateral administrative orders. Clean Water Act and Clean Air Act matters, including mobile source and new source review cases, rely heavily on agency guidance. At a time when federal agencies are pulling back on their regulatory frameworks, and repealing individual regulations, let alone promulgating new ones, the agencies’ inability to rely on guidance could have far-reaching implications for their enforcement efforts.