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, as it exceeds the powers granted to Congress under the Constitution. The Act emphasizes the state's right to regulate emissions standards for vehicles not engaged in interstate commerce, as protected by the Tenth Amendment.

Additionally, the bill defines "exempt engines" as those that operate solely within Arkansas and do not require diesel exhaust fluid. It prohibits state entities from enforcing any federal diesel regulations that infringe on the rights associated with exempt engines. Violations of this subchapter by state entities could result in civil penalties and suspension of enforcement authority, while public officials found in violation would face termination and a five-year prohibition from public office or state employment.