49 U.S.C. § 45103: Prohibited service

An individual may not use alcohol or a controlled substance after October 28, 1991 , in violation of law or a United States Government regulation and serve as an airman, crewmember, airport security screening employee, air carrier employee responsible for safety-sensitive functions (as decided by the Administrator of the Federal Aviation Administration), or employee of the Administration with responsibility for safety-sensitive functions. Notwithstanding subsection (a) of this section, an individual found to have used alcohol or a controlled substance after October 28, 1991 , in violation of law or a Government regulation may serve as an airman, crewmember, airport security screening employee, air carrier employee responsible for safety-sensitive functions (as decided by the Administrator), or employee of the Administration with responsibility for safety-sensitive functions only if the individual completes a rehabilitation program described in section 45105 of this title . used the alcohol or controlled substance when on duty; began or completed a rehabilitation program described in section 45105 of this title before using the alcohol or controlled substance; or refuses to begin or complete a rehabilitation program described in section 45105 of this title after a finding by the Administrator under this section.