The Thrift Savings Plan on Monday began requiring enrollees to identify themselves using new account numbers rather than Social Security numbers, prompting concern from some participants who say they have not received or have lost the new numbers.

TSP officials announced the switch from Social Security numbers in August, noting that participants would have to use new account numbers in conjunction with Web passwords for online transactions. Plan officials alerted participants they would receive the new numbers by mail in September.

Trabucco said people who call the ThriftLine service will now receive a message that directs them to the Web site to request that their number be reissued. Participants also can ask for their account number or a new password directly through the Account Access portion of the Web site, he said

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According to TSP: For security reasons, the TSP does not give out account numbers by telephone or e-mail.  So be sure your TSP address of record is correct before you make your request.