49 C.F.R. § 383.21 : Transportation — OTHER REGULATIONS RELATING TO TRANSPORTATION — FEDERAL MOTOR CARRIER SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION — FEDERAL MOTOR CARRIER SAFETY REGULATIONS — COMMERCIAL DRIVER'S LICENSE STANDARDS; REQUIREMENTS AND PENALTIES — SINGLE LICENSE REQUIREMENT — Number of drivers' licenses
No person who operates a commercial motor vehicle shall at any time have more than one driver's license.