Follow-up testing is unannounced drug and/or alcohol testing of an employee who has returned to safety-sensitive work after a violation. The SAP sets the plan (49 CFR 40.307):

• At least six unannounced tests in the first 12 months of safety-sensitive duty.
• The SAP may require more tests and may extend testing for up to 48 more months (five years in total).
• The employer decides the actual test dates and must not tell the employee the schedule.
• The plan follows the employee to new employers and through breaks in service.

Follow-up tests are in addition to random testing. Drug follow-up tests are directly observed.