Builder demanding additional ₹3 lakh before final possession in Pune?

I booked a flat in Pune two years ago and paid 90% of the amount. Now the builder is asking for ₹3 lakh more citing increased material costs, refusing possession otherwise. I feel betrayed as there was no mention of such costs earlier. The possession date is next month and I’m really stressed. What are my legal options under the Maharashtra RERA? Can I take this to consumer court?