The Department of Transportation, or DOT, has laws that regulate aviation (FAA), commercial motor vehicle (FHWA), railroad (FRA), mass transit (FTA), pipeline (RSPA), and maritime (USCG) vehicles. Before a company can request drug testing for their employees, one or more of the following conditions must exist:

1. Pre-employment - drug testing make take place before the applicant is hired and placed in a safety-sensitive function. This can also apply to an employee transferring to a safety-sensitive position from a non-safety sensitive position.
2. Post-accident - drug testing can be requested if an accident occurs. This is typically done if there is a death, a moving traffic violation, or when one of the injuries needs to be taken care of at a hospital.
3. Reasonable cause - drug testing may be permitted if a trained observer perceives behavior that could be indicative of drug use.
4. Random - drug testing is indiscriminately done in work places.
5. Return-to-duty - performed on employees who have previously had drug issues and are returning to work after violating an alcohol or drug policy.
6. Follow-up - mainly an indiscriminate and unannounced drug test for employees who have previously tested positive. These employees may be tested for up to five years, and they are required by law to be tested at least six times within the first year.