As of 2015, the telephone number listed on the Transportation Security Administration's website for the Transportation Worker Identification Credential is 855-347-8371. Instructions for applying for TWIC, as well as a section of frequently asked questions, is available at TSA.gov.
Maritime workers whose jobs require access to secure U.S. maritime vessels and facilities are required to have a TWIC under the Maritime Transportation Security Act. Workers who are licensed by the U.S. Coast Guard must also have the credential. The TSA recommends that these workers contact the U.S. Coast Guard directly for answers about using their TWIC cards and the requirements for accessing facilities.