Employees are expected to notify their supervisors in all instances at the earliest time practical when they are to be absent for sickness or emergency. Absences other than sickness or emergency shall be arranged as set forth in sections dealing with specific types of leave. Absence following or preceding a vacation period must be fully explained and substantiated before sick leave will be allowed. (Classified employees must be eligible for and participating in PERSI to be covered in this section of Board Policy.)