In the event a certified employee, or an employee serving a probationary period subsequent to promotion from a position in which the employee was certified, requests voluntary reduction as a result of his/her pending layoff, the certified employee shall be preferred in seniority order over
for any current vacant position in a lower class within the same department which the employee is then incumbent as the time of the layoff.
Ill. Admin. Code tit. 80, § 620.1040