5 CFR § 581.105 - Exclusions.
In determining the amount of any “moneys due from, or payable by, the United States” to any individual, there shall be excluded amounts which:
(a) Are owed by the individual to the United States, except that an indebtedness based on a levy for income tax under section 6331 of title 26 of the United States Code, shall not be excluded in complying with legal process for the support of minor children if the legal process was entered prior to the date of the levy;
(b) Are required by law to be deducted from the remuneration or other payment involved, including, but not limited to:
(1) Amounts withheld from benefits payable under title II of the Social Security Act where the withholding is required by law;
(2) Federal employment taxes;
(3) Amounts mandatorily withheld for the United States Soldiers' and Airmen's Home;
(4) Fines and forfeitures ordered by a court-martial or by a commanding officer; and
(5) Amounts deducted for Medicare;
(c) Are properly withheld for Federal, State, or local income tax purposes, if the withholding of the amounts is authorized or required by law and if amounts withheld are not greater than would be the case if the individual claimed all dependents to which he/she were entitled. The withholding of additional amounts pursuant to section 3402(i) of title 26 of the United States Code may be permitted only when the individual presents evidence of a tax obligation which supports the additional withholding;
(d) Are deducted as health insurance premiums, including, but not limited to, amounts deducted from civil service annuities for Medicare where such deductions are requested by the Health Care Financing Administration;
(e) Are deducted as normal retirement contributions, not including amounts deducted for supplementary coverage. For purposes of this section, all amounts contributed under sections 8351 and 8432(a) of title 5 of the United States Code to the Thrift Savings Fund are deemed to be normal retirement contributions. Amounts withheld as Survivor Benefit Plan or Retired Serviceman's Family Protection Plan payments are considered to be normal retirement contributions. Except as provided in this paragraph, amounts voluntarily contributed toward additional retirement benefits are considered to be supplementary; or
(f) Are deducted as normal life insurance premiums from salary or other remuneration for employment, not including amounts deducted for supplementary coverage. Both Servicemen's Group Life Insurance and “Basic Life” Federal Employees' Group Life Insurance premiums are considered to be normal life insurance premiums; all optional Federal Employees' Group Life Insurance premiums and life insurance premiums paid for by allotment, such as National Service Life Insurance, are considered to be supplementary.