41 CFR § 301-52.23
Is the additional fee, which is equal to any late payment charge that the card contractor would have been able to charge had I not paid the bill, considered income?
June 9, 2020
Yes, your agency will report this payment as additional wages on Form W-2.
[FTR Amdt. 90, 65 FR 3056, Jan. 19, 2000]