49 CFR §382.501

1. (a)Except as provided in subpart F of this part, no driver shall perform safety-sensitive functions, including driving a commercial motor vehicle, if the driver has engaged in conduct prohibited by subpart B of this part or an alcohol or controlled substances rule of another DOT agency.
2. (b)No employer shall permit any driver to perform safety-sensitive functions, including driving a commercial motor vehicle, if the employer has determined that the driver has violated this section.
3. (c)For purposes of this subpart, commercial motor vehicle means a commercial motor vehicle in commerce as defined in § 382.107, and a commercial motor vehicle in interstate commerce as defined in part 390 of this subchapter.