49 U.S.C. § 45103

1. (a)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.
2. (b)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.
3. (c)An individual who served 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 and who was found by the Administrator to have used alcohol or a controlled substance after October 28, 1991, in violation of law or a Government regulation may not carry out the duties related to air transportation that the individual carried out before the finding of the Administrator if the individual—
   1. (1)used the alcohol or controlled substance when on duty;
   2. (2)began or completed a rehabilitation program described in section 45105 of this title before using the alcohol or controlled substance; or
   3. (3)refuses to begin or complete a rehabilitation program described in section 45105 of this title after a finding by the Administrator under this section.