the employee has completed at least 2 years of continuous service in 1 or more civil service positions located in a territory or possession of the United States, the Commonwealth of Puerto Rico, or the Commonwealth of the Northern Mariana Islands;

the agency determines that replacing the employee with another employee possessing the required qualifications and experience would be difficult; and

the agency determines it is in the best interest of the Government to encourage the employee to complete a specified additional period of employment with the agency in the territory or possession, the Commonwealth of Puerto Rico or Commonwealth of the Northern Mariana Islands, except that the total amount of service performed in a particular territory, commonwealth, or possession under 1 or more agreements established under this section may not exceed 5 years.

an amount equal to 25 percent of the annual rate of basic pay of the employee at the beginning of the service period, times the number of years in the service period; or

$15,000 per year in the service period.

Payment of an extended assignment incentive shall be contingent upon the employee entering into a written agreement with the agency specifying the period of service and other terms and conditions under which the extended assignment incentive is payable.

The agreement shall set forth the method of payment, including any use of an initial lump-sum payment, installment payments, or a final lump-sum payment upon completion of the entire period of service.

The agreement shall describe the conditions under which the extended assignment incentive may be canceled prior to the completion of agreed-upon service period and the effect of the cancellation. The agreement shall require that if, at the time of cancellation of the incentive, the employee has received incentive payments which exceed the amount which bears the same relationship to the total amount to be paid under the agreement as the completed service period bears to the agreed-upon service period, the employee shall repay that excess amount, at a minimum, except that an employee who is involuntarily reassigned to a position stationed outside the territory, commonwealth, or possession or involuntarily separated (not for cause on charges of misconduct, delinquency, or inefficiency) may not be required to repay any excess amounts.