20 CFR 220.161: How work affects an employee disability annuity.

In addition to the condition in § 220.160, the employee's disability annuity is not payable and the employee must return the annuity payment for any month in which the employee earns more than $400 (after deduction of impairment-related work expenses) in employment or self-employment of any kind. Any annuity amounts withheld because the annuitant earned over $400 in a month may be paid after the end of the year, as shown in § 220.164. The $400 monthly limit no longer applies when the employee attains retirement age and the disability annuity is converted to a full age annuity. See § 220.145 for the definition of impairment-related work expenses.