20 C.F.R. § 220.175 Responsibility to notify the Board of events which affect disability.
Title 20 - Employees' Benefits
If the annuitant is entitled to a disability annuity because he or she is disabled for any regular employment, the annuitant should promptly tell the Board if— (a) His or her impairment(s) improves; (b) He or she returns to work; (c) He or she increases the amount of work; or (d) His or her earnings increase.
Title 20: Employees' Benefits
PART 220—DETERMINING DISABILITY
Subpart O—Continuing or Stopping Disability Due to Substantial Gainful Activity or Medical Improvement
§ 220.175 Responsibility to notify the Board of events which affect disability.

