From the Postal Bulletin dated September 13, 2007
In August 2007, Thrift Savings Plan (TSP) management sent a letter to all participants announcing the implementation of new security enhancements.
Starting in October 2007, the TSP will no longer use your Social Security number as your primary identifier on its Web site, www.tsp.gov, or ThriftLine, 877-968-3778. Instead, TPS will assign an account number for you to use in conjunction with your Web site TSP password or ThriftLine personal identification number (PIN). You will also use your new account number when you fill out TSP forms.
During September 2007, TSP will send the account number to you in a bright blue mailer. If your address on file with the Postal Service™ has changed, make sure to update it using one of the following options:
1. On a Postal Service computer, go to http://blue.usps.gov; under “Employee Resources” in the right-hand column, click on Employee Self-Service, then click on Employee Change of Address.
2. On a Postal Service kiosk, click on Employee Change of Address.
3. By mail, send PS Form 1216, Employee’s Current Mailing Address, to:
HRSSC COMPENSATION AND BENEFITS
PO BOX 970400
GREENSBORO NC 27497-0400
4. By telephone, call HRSSC at 877-477-0323, option 5; validate your identity with your employee identification number (EIN) or Postal Service PIN.
Related: Account Numbers Are Coming in October (TSP website)