It’s always worth knowing every source of retirement or disability money. While most are familiar with regular Social Security, there are some workers who do not pay into this system. These can include government workers, military personnel, railroad workers and many teachers and even your local postal delivery person! These workers pay into a different system, and may not be fully eligible for Social Security for the years they did so.
If you have ever paid your taxes into the Social Security system in your lifetime of work, there may be eligibility. Some Federal employees and employees of State or local government agencies may be eligible for pensions that are based on earnings not covered by Social Security.
If you didn’t pay Social Security taxes on your government earnings and you are eligible for Social Security benefits, the formula used to figure your benefit amount may be modified, giving you a lower Social Security benefit.
There is a vast amount of information about “windfall offsets” at this link: http://www.ssa.gov/gpo-wep/