How a pension affects your Social Security retirement benefit

If your pension is from work where you paid Social Security taxes, it will not affect the amount of your Social Security benefit. Pensions based on work that is not covered by Social Security (for example, the Federal civil service and some State or local government agencies) probably will cause the amount of your Social Security benefit to be reduced. This type of benefit reduction is called the Windfall Elimination Provision (WEP).

See here for details : http://ssa-custhelp.ssa.gov/cgi-bin/ssa.cfg/php/enduser/std_adp.php?p_fa...