Section 25(5) in The Rajasthan Municipal Service Rules, 1963
(5)selection for promotion on the post included in the service shall be made on the basis of seniority-cum-merit:Provided that promotion on the highest post in the service if it is at least third promotion shall be made on the basis of merit alone:Provided further that if the Committee is satisfied that suitable persons are not available for selection by promotion to the highest post(s) strictly on the basis of merit in a particular year selection by promotion to the highest post(s) on the basis of seniority cum merit may be made in the same manner as specified in these rules.
