In Michigan et al. v. Environmental Protection Agency (EPA) and Perez, Secretary of Labor v. Mortgage Bankers Association (MBA), the US Supreme Court dealt with concerned two specific issues. The first was whether and to what extent administrative agencies should account for costs when engaging in environmental regulation. As for the second, it sought to ascertain whether agencies should adopt notice-and-comment rulemaking procedures when amending or repealing their interpretations of existing regulations. To address these issues, the Court — albeit indirectly — returned to recurring questions of US administrative law, such as how to interpret the deference doctrine and the extent of agencies’ procedural accountability. This article provides a critical analysis of the judgments and highlights their systemic consequences, focusing especially on the application of the Chevron doctrine and on the limits of judicial deference, in light of the principle of checks and balances.