46 C.F.R. § 16.250

(a) The marine employer must require any crewmember engaged or employed on board a vessel owned in the United States that is required by law or regulation to engage, employ or be operated by an individual holding a credential issued under this subchapter, who is reasonably suspected of using a dangerous drug to be chemically tested for dangerous drugs.

(b) The marine employer's decision to test must be based on a reasonable and articulable belief that the individual has used a dangerous drug based on direct observation of specific, contemporaneous physical, behavioral, or performance indicators of probable use. Where practicable, this belief should be based on the observation of the individual by two persons in supervisory positions.

(c) When the marine employer requires testing of an individual under the provisions of this section, the individual must be informed of that fact and directed to provide a urine specimen as soon as practicable. This fact will be entered in the vessel's official logbook, if one is required.

(d) If an individual refuses to provide a urine specimen when directed to do so by the employer under the provisions of this section, this fact will be entered in the vessel's official logbook, if one is required.