there appears to be some rationale behind such imposition
firstly the member who has given his flat on rent is not before the society at all times
whereas the members using their flats for self occupation are within the society premises only
so compared to a member who lives in the society and defaults in payment of maintenance AND a member who does not live in the society and has given his flat on rent, it will be difficult for the society to go behind the member of the latter class than the former class
this appears to me to be the reason why the society has come up with such a rule
if the rationale of the society is as above then it is a reasonable restriction and hence legal
the advance maintenance would also be charged to ensure that if in case the member's tenant does something which causes any damage to the society's property or its common areas then in absence of the member, the society can use the advance maintenance to make good the said damage. Ofcourse the society will be within its right to charge separately to the member for making good such damage by his tenant. The advance only gives an immediate fund in the hands of the society to meet such contingencies
considering the above i dont see any illegality in the society's decision
you can very well make the payment of the advance at one go from one month's rental that your tenant would pay you