The Arkansas Diesel Engine Freedom Act of 2025 aims to prohibit state enforcement of federal regulations concerning certain diesel engines operating solely within the state. The bill asserts that the U.S. Congress lacks the constitutional authority to regulate intrastate commerce, specifically regarding the use of diesel exhaust fluid in diesel engines. It establishes that any federal regulation mandating such use is null and void within Arkansas, thereby affirming the state's right to regulate emissions standards for vehicles not engaged in interstate commerce.

The bill introduces a new subchapter to the Arkansas Code, defining terms such as "exempt engine" and "exempt engine right," and outlines the rights associated with exempt engines. It also stipulates that state entities cannot enforce federal diesel regulations that infringe on these rights and establishes penalties for violations, including civil penalties and suspension of enforcement authority for state agencies. Additionally, public officials found in violation may face termination and a prohibition from holding public office for five years.