(a) General rule.--Seniority is established for the classified service, classification series and for each class, unless there is in existence a labor agreement covering the position in the classified service, in which case the definition of seniority in the labor agreement shall control.
(b) Calculation of seniority.--
(1) Seniority for the classified service begins with the date of first civil service employment in a civil service class and includes periods of subsequent employment in any civil service class, providing the employment has been on a continuous basis.
(2) Seniority for a classification series begins with the date of first civil service employment in the class series and includes periods of employment in classes within the series during any period while employed on a continuous basis in the classified service.
(3) Seniority in each class begins with the date of first civil service employment in that class and includes periods of subsequent employment in that class during any period while employed on a continuous basis in the classified service.
(c) Consideration of furlough and leave of absence.--Periods of furlough and approved leave of absence without pay shall be deemed continuous employment for seniority purposes, except that the period of furlough or leave of absence without pay shall not be counted toward seniority.