Section 15.401 - Employment and service within restrictions of credential(a) A person may not employ or engage an individual, and an individual may not serve, in a position in which an individual is required by law or regulation to hold a Transportation Worker Identification Credential (TWIC) and/or Merchant Mariner Credential (MMC), unless the individual holds all credentials required, as appropriate, authorizing service in the capacity in which the individual is engaged or employed, and the individual serves within any restrictions placed on the credential. An individual holding an active MMC issued by the Coast Guard must also hold a valid TWIC issued by the Transportation Security Administration unless the individual is exempt under 46 CFR 10.203(b)(1) .(b) A person may not employ or engage an individual, and an individual may not serve in a position in which it is required by law or regulation that the individual hold an MMC endorsed with a national endorsement, as well as a corresponding STCW endorsement for service outside the boundary line.(c) A person may not employ or engage an individual in a position required to hold an MMC unless that individual maintains a current medical certificate. Medical certificates must be issued and will remain current for the following periods of time, unless otherwise noted on the certificate: (1) Two years for individuals serving on vessels to which STCW applies unless the mariner is under the age of 18, in which case the maximum period of validity will be 1 year.(2) Five years for all other mariners.(d) Each individual referred to in paragraph (a) of this section must hold an MMC that serves as identification, with an appropriate endorsement for the position in which the seaman serves, and the MMC, along with a valid medical certificate, must be presented to the master of the vessel at the time of employment or before signing Articles of Agreement.(e) Each individual below the grades of officer and staff officer employed on any U.S. flag merchant vessel of 100 GRT or more must possess a valid MMC issued by the Coast Guard, except as noted below:(1) Mariners on vessels navigating exclusively on rivers and lakes, except the Great Lakes, as defined in § 10.107 of this subchapter.(2) Mariners below the rank of officer employed on any non-self-propelled vessel, except seagoing barges and barges to which 46 U.S.C. chapter 37 applies.(3) Personnel not designated with any safety or security duties onboard casino vessels.(f) Every person employed on a vessel with dual tonnages (both domestic and international) must hold a credential authorizing service appropriate to the tonnage scheme under which the vessel is manned and operating.USCG-2004-17914,78 FR 17914, Dec. 24, 2013, as amended by USCG-2020-0069, 87 FR 66591, Nov. 4, 2022