IT company wants bonus back after fnf settled

Hello,
I worked in IT company in Pune with 500-1000 employees and given the best. Left the company 2.5 months back and got fnf and release letter done. Now suddenly company is asking for bonus back which I talked with Account Manager was company bonus. I received a mail threatning to return 90K INR or there will be no form16 and back ground verification issue with later company. I am of opinion I earned it but can they take a step like this. Please guide.

Hi,

I think you are referring bonus which is received by you towards project completed or some special assignment completed? It amount paid is for past contribution employer has no right to ask it back