Under 5 U.S.C. 5538, employing agencies must pay differential payments to eligible Federal civilian employees who are members of the Reserve or National Guard (hereafter referred to as "reservists") called or ordered to active duty under certain specified provisions of law. Federal agencies must provide a payment—a "reservist differential"—equal to the amount by which an employee’s projected civilian "basic pay" for a covered pay period exceeds the employee’s actual military "pay and allowances" allocable to that pay period.

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