The Arkansas Diesel Engine Freedom Act of 2025 aims to prohibit state enforcement of federal regulations concerning certain diesel engines, specifically those operating solely within the state. The bill asserts that the U.S. Congress lacks the constitutional authority to regulate intrastate commerce, including mandates requiring the use of diesel exhaust fluid in diesel engines. It emphasizes the state's right under the Tenth Amendment to regulate emissions standards for vehicles not engaged in interstate commerce and declares any conflicting federal regulations as null and void.

The bill introduces a new subchapter to the Arkansas Code, defining terms such as "exempt engine" and "federal diesel regulation," and establishes that state entities cannot enforce federal regulations that infringe on the rights associated with exempt engines. It also outlines penalties for state entities that violate this subchapter, including civil penalties and suspension of enforcement authority for state agencies. Public officials or representatives found in violation would face termination and a five-year prohibition from public office or state employment.