A repayment is a returned payment, a cash refund, or an amount withheld for overpayment purposes.
Under the Internal Revenue Code, the RRB is allowed to give repayment credit for the SSEB and/or pre-SSEB portion of tier I for any tax year. Refer to IRS Publication 915, "Social Security and Equivalent Railroad Retirement Benefits", for information regarding current tax year or prior tax year's SSEB repayment.
The NSSEB portion of tier I and tier II repayments are composed of taxable and nontaxable portions. There are tax implications when considering NSSEB tier II repayments. Therefore, the way you will handle the repayment will depend on the tax years to which the repayment applies, and whether you had included the benefits that you repaid in your gross income for those tax years. Refer to IRS Publication 575, "Pension and Annuity Income", for information regarding NSSEB, tier II , Vested Dual Benefits, and SUPP repayments as well as instructions on how to handle current tax year and prior tax years' repayments for income tax purposes.