Subject to subsection (b), effective at the beginning of the first applicable pay period commencing on or after the first day of the month in which an adjustment takes effect under
section 5303 of this title in the rates of pay under the General Schedule, the annual rate of pay for positions at each level of the Executive Schedule shall be adjusted by an amount, rounded to the nearest multiple of $100 (or if midway between multiples of $100, to the next higher multiple of $100), equal to the percentage of such annual rate of pay which corresponds to the most recent percentage change in the ECI (relative to the date described in the next sentence), as determined under section 704(a)(1) of the Ethics Reform Act of 1989. The appropriate date under this sentence is the first day of the fiscal year in which such adjustment in the rates of pay under the General Schedule takes effect.