(1) An employee shall contribute the minimum number of hours required under subsection (a)(2)(A), if such employee is an employee
(A) for less than 3 years of service and contributes a minimum of 4 hours;
(B) for between 3 years and less than 15 years of service and contributes a minimum of 6 hours; or
(C) for 15 years or more of service and contributes a minimum of 8 hours.
(2) Notwithstanding the provisions of paragraph (1), the Leave Bank Board of an agency, after consultation with the Office of Personnel Management, may
(A) reduce the minimum number of hours required under paragraph (1) for any leave year, if such Board determines there is a surplus of leave in the leave bank; and
(B) increase the number of minimum hours required under paragraph (1) for the succeeding leave year, in any leave year in which the Board determines there is a shortage of leave in the leave bank.