Non-payment of Variable Pay (Annual Variable Compensation) by my erstwhile employer

Hi, I would like to bring to your notice a concern with regards to the non-payment of variable pay/annual variable compensation by my erstwhile employer. I was employed with my erstwhile employer (IT Sector) located in Pune for little over a year (from Feb 14 2019 thru Apr 09 2020). I have resigned from duties on 11th January 2020 and got relieved from duties on Apr 09 2020 after serving the mandated notice period of three months. The company pays the variable payout annually along with the March salary. The company withholds the variable pay component for the months Jan thru Dec and is paid along with the March salary in the subsequent year.I have not received the variable pay and I later got to know that as per company's policy, employees are not eligible for variable pay if serving notice period as on the payment date. As I was in notice period during that time, I did not receive the variable pay. Also please note that there was no mention of this criteria/policy in the Offer Letter. My concern here is that is it lawfully correct and legal to tie any of the employees remuneration including that of variable pay and/or other benefits to employee resignation. I firmly believe that there should not be any components of the employees remuneration (salary package) tied to the employee resignation as part of company's policy. I hereby, would like to seek your advice/guidance/opinion/suggestion if any, on this matter and would like to know if such a policy is lawfully correct and legal. Looking forward to hear from you at the earliest.. Thanks Sivaram