5 CFR 1620.35: Loan payments.

NAF instrumentalities must deduct and transmit TSP loan payments for employees who elect to be covered by CSRS or FERS to the TSP record keeper in accordance with 5 CFR part 1655 and the TSP record keeper's procedures. Loan payments may not be deducted and transmitted for employees who elect to be covered by the NAF retirement system. Such employees will be considered to have separated from Government service and may continue making loan repayments in accordance with 5 CFR part 1655 and the TSP record keeper's procedures.