What is the Special Retirement Supplement?
It is an addition to a FERS annuity that estimates the Social Security benefits earned through federal or postal employment under FERS; it is intended to replicate the Social Security benefit payable for that period of service at age 62. The following classes of employees are entitled to the supplement:

• Law enforcement officers, air traffic controllers, and firefighters.
• Voluntary retirees at the minimum retirement age with at least 30 years of service or at age 60 with at least 20 years of service.
• Discontinued service retirees when the retiree attains the minimum retirement age.
• Military Reserve technicians who are age 50 with at least 25 years of service who lose their military status.

The supplement can be reduced if you have outside earnings in certain circumstances. See Chapter 3, Section 4 of the Federal Employees Almanac for details.