5 C.F.R. § 839.411

What can I elect if I was put in FERS by mistake?

Read at: eCFRecfr.gov CornellLII GovInfogovinfo.gov CasesGoogle Scholar

If you were placed in FERS due to a qualifying retirement coverage error and you should have been in CSRS, you may elect FERS or CSRS. If you were placed in FERS due to a qualifying retirement coverage error and you should have been in CSRS Offset, you may elect FERS or CSRS Offset. If you were placed in FERS due to a qualifying retirement coverage error and you should have been in Social Security-Only, you may elect FERS or Social Security-Only. This is summarized in the following chart:

You are in:And you belong in:You may elect:
FERSCSRSFERS or CSRS.
FERSCSRS OffsetFERS or CSRS Offset.
FERSSocial Security-OnlyFERS or Social Security-Only.