33 CFR §95.035

1. (a)Only a law enforcement officer or a marine employer may direct an individual operating a vessel to undergo a chemical test when reasonable cause exists. Reasonable cause exists when:
   1. (1)The individual was directly involved in the occurrence of a marine casualty as defined in Chapter 61 of Title 46, United States Code, or
   2. (2)The individual is suspected of being in violation of the standards in §§ 95.020 or 95.025.
2. (b)When an individual is directed to undergo a chemical test, the individual to be tested must be informed of that fact and directed to undergo a test as soon as is practicable.
3. (c)When practicable, a marine employer should base a determination of the existence of reasonable cause, under paragraph (a)(2) of this section, on observation by two persons.