Is Payment Of Gratuity Mandatory Or Optional?

I had worked as a lecturer in a Educational Institute for 9 years and left to join another Institute. Along with me several others also left & joined this new Institute. The Head of the Earlier institute had instructed the office not to entertain any requests from the people who had left. As they would not pay or process the PF & Gratuity applications a group of people approached the court for remedy.
Now the situation is they have paid the PF (after 10 yrs)but the office staff say that they have been asked not to process the application for Gratuity.
Now the question is can they refuse to pay Gratuity ?

No they cannot. Not under the circumstances you have mentioned. Of course, the operative word would be - were you "employees" for these 9 years? Since PF was paid eventually, I am sure you were.
The 10 year delay in releasing PF sort of tells me that you and your friends did not follow it up the right way, nor did you proceed with it in the manner prescribed.
There are multiple threads on the concepts of gratuity. Request you to do a very basic search and you will be surely inundated by the same.
All the best.

If it helps, please have a look at the attachments posted by Prem Singh Rawat at
https://www.citehr.com/147034-gratui...-laws-pg2.html