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 establishes that such federal regulations are null and void within Arkansas, emphasizing the state's right to regulate emissions standards under the Tenth Amendment. The act also defines "exempt engines" as those that do not require diesel exhaust fluid and are operated solely within the state.

Additionally, the bill outlines the rights associated with exempt engines, stating that state entities cannot enforce federal regulations that infringe upon these rights. It allows for the lawful manufacture, sale, and installation of exempt engines within Arkansas, provided they are labeled for in-state use and not exported unless compliant with federal laws. Violations of this act by state entities can result in civil penalties and suspension of enforcement authority, while public officials involved may face termination and a five-year prohibition from public office or state employment.