1. The decision to hike the monthly maintenance fee on the basis of plinth area of the apartment has to be passed by the society in its general meeting or AGM having the requisite quorum.
2. Maintenance charges levied by any society are for the purpose of maintenance, repairs and reconstruction of the common infrastructure of the society, like, society's premises, security arrangements, supply lines, sewer lines, lifts, staircases, etc. as these are commonly used by apartment owners. In such a scenario, to quantify maintenance charges on the basis of plinth area of the apartment is wholly illegal. As such, you may refuse to pay the differential charges and challenge the decision of the society in the court.