Penalty Amount for Delayed Maintenance Payment to Apartment Association

The maintenance fee is collected in advance for 3 months. Every owner also deposited 4+ lakhs as corpus. They want a penalty for un-availed service. (1) Recently the MC passed a rule that a fixed penalty Rs.500 to be paid for delay from one day to one month, which works out to 85% per year . Is there any limit to this kind of penalty ? (2) The amount is also flat while maintenance amount for flats vary from 20,000 to 40,000, thus over-charging the owners having smaller sized flat. Can the MC bring such unequal rule ? (3) As I know, the above such practices are not there in any apartment to my knowledge. The MC did not take the approval of the owners for this change of rule. When asked, the MC reply is as follows for the above order of questions: 1) Advance fees is charged to pay the coming month expenses. Such penalties are imposed to inculcate discipline. 2) Due to administrative difficulties, a flat penalty is imposed. 3) For penalty collection, owners need not be consulted. Request the legal views of such autocratic rulings by the MC.