HRA claim and document proof requiured

Can anyone please reply for my query.

Hi,
Apart from rent receipts, my employer is insisting on production of agreement with landlord duly REGISTERED with the registration dept of revenue authorities by paying stamp duty registration fees.
I have produced rent receipts and agreement with landlord which is not registered. But they refused to allow hra rebate. Please let me know whether his action is correct or not. If not, what is the solution to get HRA rebate. Can I claim refund from Income tax authorities?