Not all states intend to include greenhouse gases in their State Implementation Plans. On August 2, 2010, the Attorney General for the State of Texas and the Chairman of the Texas Commission of Environmental Quality jointly sent a strongly worded letter to EPA, stating that Texas "has neither the authority nor the intention of interpreting, ignoring, or amending its laws in order to compel the permitting of greenhouse gas emissions."

Mirroring claims Texas has asserted in its pending legal challenge to the Tailoring Rule in the U.S. Court of Appeals for the D.C. Circuit, the officials took issue with nearly every aspect of the Tailoring Rule—including EPA's authority to issue the rule, the scientific studies that EPA relied on in support of the rule, EPA's rulemaking procedures, and the legality of the rule itself under applicable environmental laws. Specifically, Texas took the position that the Clean Air Act precludes regulation of greenhouse gases, that EPA lacks the statutory authority to regulate greenhouse gases on its own, and that compliance with the Tailoring Rule would violate Texas law. The letter further argues that EPA failed to follow the formal rulemaking procedures set forth in § 307 of the Clean Air Act in promulgating the Tailoring Rule and that the rule fails to include "any evidence that [the rule] would achieve specific results."