49 CFR §655.35

1. (a)No employer shall permit a covered employee tested under the provisions of subpart E of this part who is found to have an alcohol concentration of 0.02 or greater but less than 0.04 to perform or continue to perform safety-sensitive functions, until:
   1. (1)The employee's alcohol concentration measures less than 0.02; or
   2. (2)The start of the employee's next regularly scheduled duty period, but not less than eight hours following administration of the test.
2. (b)Except as provided in paragraph (a) of this section, no employer shall take any action under this part against an employee based solely on test results showing an alcohol concentration less than 0.04. This does not prohibit an employer with authority independent of this part from taking any action otherwise consistent with law.