(a) Pursuant to section 208(b) of the act of September 1, 1954 (68 Stat. 1111), nothing in this subpart relating to the payment of premium pay on an annual basis may be construed to decrease the existing aggregate rate of pay of an employee on the rolls of an agency immediately before the date section 5545(c) of title 5, United States Code, is made applicable to him by administrative action.

(b) When it is necessary to determine an employee's existing aggregate rate of pay (referred to in this section as existing aggregate rate), an agency shall determine it on the basis of the earnings the employee would have received over an appropriate period (generally 1 year) if his tour of duty immediately before the date section 5545(c) of title 5, United States Code, is made applicable to him had remained the same. In making this determination, basic pay and premium pay for overtime, night, holiday, and Sunday work are included in the earnings the employee would have received. Premium pay for irregular or occasional overtime work may be included only if it was of a significant amount in the past and the conditions which required it are expected to continue.

(c) An agency shall recompute an employee's rate of pay based on premium pay on an annual basis when he received subsequent increases in his rate of basic pay in order to determine whether or not the employee should continue to receive an existing aggregate rate or be paid premium pay on an annual basis.

(d) Except as otherwise provided by statute, an agency may not use subsequent increases in an employee's rate of basic pay to redetermine or increase the employee's existing aggregate rate. However, these increases shall be used for other pay purposes, such as the computation of retirement deductions and annuities, payment of overseas allowances and post differentials, and determination of the highest previous rate under part 531 of this chapter.

(e) When an agency elects to pay an employee premium pay on an annual basis, he is entitled to continue to receive hourly premium pay properly payable under sections 5542, 5543, 5545 (a) and (b), and 5546 of title 5, United States Code, until his base pay plus premium pay on an annual basis equals or exceeds his existing aggregate rate. When this occurs, the agency shall pay the employee his base pay plus premium pay on an annual basis.

(f) Except when terminated under paragraph (e) of this section, an agency shall continue to pay an employee an existing aggregate rate so long as:

(1) He remains in a position to which §550.141, §550.151, or §550.162(c) is applicable;

(2) His tour of duty does not decrease in length; and

(3) He continues to perform equivalent night, holiday, and irregular or occasional overtime work.

(g) If an employee who is entitled to an existing aggregate rate moves from one position to another in the same agency, both of which are within the scope of section 5545(c) of title 5, United States Code, he is entitled to be paid an existing aggregate rate in the new position such as he would have received had he occupied that position when the agency elected to make section 5545(c) applicable to it.