Can’t sign off the job for next 3 month from the date appraisal made.

Hello Everyone,
I am working as an HR Executive in a Startup IT Company. I was asked to modify the Performance appraisal policy of my company. Can I add a point in the policy that *the employee can't sign off the job for the next 3 month from the date appraisal made and if they do so then the company will not provide the experience/relieving letter to the member*
Kindly through a light to my query.
Thank you

What is the rationale behind such a clause?
Such clauses are not legally sustainable.
Company can retain employees and lower employee turnover by employee friendly and progressive policies only.
Such restrictions will only make employees find other ways to overcome.No employee can be held by compulsion.

Thank you Nathrao for your suggestion!