49 C.F.R. § 219.105
Railroad's duty to prevent violations
(a) A railroad may not, with actual knowledge, permit a regulated employee to go or remain on duty in regulated service in violation of the prohibitions of § 219.101 or § 219.102. As used in this section, the actual knowledge imputed to the railroad is limited to that of a railroad management employee (such as a supervisor deemed an “officer,” whether or not such person is a corporate officer) or a supervisory employee in the offending regulated employee's chain of command. A railroad management or supervisory employee has actual knowledge of a violation when he or she:
(1) Personally observes a regulated employee use or possess alcohol or use drugs in violation of this subpart. It is not sufficient for actual knowledge if the supervisory or management employee merely observes the signs and symptoms of alcohol or drug use that require a reasonable suspicion test under § 219.301;
(2) Receives information regarding a violation of this subpart from a previous employer of a regulated employee, in response to a background information request required by § 40.25 of this title; or
(3) Receives a regulated employee's admission of prohibited alcohol possession or prohibited alcohol or drug use.
(b) A railroad must exercise due diligence to assure compliance with §§ 219.101 and 219.102 by each regulated employee.
(c) A railroad's alcohol and/or drug use education, prevention, identification, intervention, and rehabilitation programs and policies must be designed and implemented in such a way that they do not circumvent or otherwise undermine the requirements, standards, and policies of this part. Upon FRA's request, a railroad must make available for FRA review all documents, data, or other records related to such programs and policies.
(d) Each year, a railroad's supervisors must conduct and record a number of “Rule G” employee observations at a minimum equal to twice the railroad's total number of regulated employees. Each “Rule G” observation must be made sufficiently close to an individual regulated employee to determine whether the employee is displaying signs and symptoms indicative of a violation of the prohibitions of this part.