Interest on delayed society sinking fund & annual fees

I reside in Co-Operative Housing Society in Pune. The due date decided during AGM to pay the dues by 25/05/2016. Though some members have delayed their payment. The Managing Committee charged them Interest at certain percentage for full month though it was paid during month. e.g. Payment received on 7th June 2016. The interest charged is for whole month i.e. 1st June to 30th June. Is it legal or appropriate according to the By Laws of Co-operative Housing Society ?