No employer may allow, require, permit or authorize a driver to operate a commercial motor vehicle during any period in which an employer determines that a driver is not in compliance with the return-to-duty requirements in 49 CFR part 40, subpart O, after the occurrence of any of the following events:

1. (a) The driver receives a positive, adulterated, or substituted drug test result conducted under part 40 of this title.
2. (b) The driver receives an alcohol confirmation test result of 0.04 or higher alcohol concentration conducted under part 40 of this title.
3. (c) The driver refused to submit to a test for drugs or alcohol required under this part.
4. (d) The driver used alcohol prior to a post-accident alcohol test in violation of § 382.209.

5. (e) An employer has actual knowledge, as defined at § 382.107, that a driver has:

   1. (1) Used alcohol while performing safety-sensitive functions in violation of § 382.205;
   2. (2) Used alcohol within four hours of performing safety-sensitive functions in violation of § 382.207; or
   3. (3) Used a controlled substance, except when the use is prescribed by a licensed medical practitioner who is familiar with the driver's medical history and has advised the driver that the substance will not adversely affect the driver's ability to safely operate a commercial motor vehicle.

[81 FR 87724, Dec. 5, 2016, as amended at 88 FR 80180, Nov. 17, 2023]