In addition to annual leave, each merit system employee is entitled to up to 15 days of sick leave with pay in a calendar year. An employee may use sick leave at any time. An employee who uses 3 or more consecutive days of sick leave must present a certificate from a licensed physician before the employee may receive payment for the period of absence. An employee may accumulate unused sick leave up to 60 days or more as the Commission specifies by regulation. The Commission, by regulation, may provide for granting a leave of absence for a longer period, with full or partial pay, to an employee who is disabled through an injury or illness resulting or arising from the employee’s employment with the Commission.