49 CFR 40.15
May an employer use a service agent to meet DOT drug and alcohol testing requirements?
(a)As an employer, you may use a service agent to perform the tasks needed to comply with this part and DOT agency drug and alcohol testing regulations, consistent with the requirements of Subpart Q and other applicable provisions of this part.#
(b)As an employer, you are responsible for ensuring that the service agents you use meet the qualifications set forth in this part (e.g., § 40.121 for MROs). You may require service agents to show you documentation that they meet the requirements of this part (e.g., documentation of MRO qualifications required by § 40.121(e)).#
(c)You remain responsible for compliance with all applicable requirements of this part and other DOT drug and alcohol testing regulations, even when you use a service agent. If you violate this part or other DOT drug and alcohol testing regulations because a service agent has not provided services as our rules require, a DOT agency can subject you to sanctions. Your good faith use of a service agent is not a defense in an enforcement action initiated by a DOT agency in which your alleged noncompliance with this part or a DOT agency drug and alcohol regulation may have resulted from the service agent's conduct.#
(d)As an employer, you must not permit a service agent to act as your DER.#