The federal law that mandates random drug and alcohol testing is primarily outlined in the Omnibus Transportation Employee Testing Act of 1991. This legislation requires employers in the transportation industry, including those in aviation, trucking, railroads, and maritime sectors, to conduct random testing of employees who perform safety-sensitive functions. Under this law, employees are subject to random drug and alcohol tests throughout the year, with tests conducted on an unannounced basis to ensure integrity and compliance.​​​​

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Random Testing – CDL drivers are subject to unannounced random testing. A driver may be directed to take a drug test even when at home in an off-duty status. Random alcohol testing may occur only when the driver is on duty or immediately before or after that time. Once notified to report for random testing, the driver must immediately report to the testing location. A delayed arrival may be considered a refusal (see 49 CFR 40.191), which is equivalent to a positive test result.​​