20 C.F.R. § 404.1242
(b) Back pay under a statute. Back pay under a statute is a payment by an employer following an award, determination or agreement approved or sanctioned by a court or administrative agency responsible for enforcing a Federal or State statute protecting an employee's right to employment or wages. Examples of these statutes are:
(4) Civil Rights Act of 1964.
Payments based on legislation comparable to and having a similar effect as those listed in this paragraph may also qualify as having been made under a statute. Back pay under a statute, excluding penalties, is wages if paid for covered employment. It is allocated to the periods of time in which it should have been paid if the employer had not violated the statute. For backpay awards affecting periods prior to 1987, a State must fill a wage report and pay the contributions due for all periods involved in the back pay award under the rules applicable to those periods.
(c) Back pay not under a statute. Where the employer and the employee agree on the amount payable without any award, determination or agreement approved or sanctioned by a court or administrative agency, the payment is not made under a statute. This back pay cannot be allocated to prior periods of time but must be reported by the employer for the period in which it is paid.
(Approved by the Office of Management and Budget under control number 0960-0425)
[53 FR 32976, Aug. 29, 1988, as amended at 66 FR 28836, May 25, 2001]