(a) Deduction by salary offset, from an employee's disposable current pay, shall be subject to the following circumstances:

(1) When funds are available, the Board will collect debts owed the United States in full in one lump-sum. If funds are not available or the debt exceeds 15% of disposable pay for an officially established pay interval, collection will normally be made in installments.

(2) The installments shall not exceed 15% of the disposable pay from which the deduction is made, unless the employee has agreed in writing to a larger amount.

(3) Deduction will commence with the next full pay interval following notice that deductions will commence.

(4) Installment deductions will not be made over a period greater than the anticipated period of employment.