Hi Suman... This is a very common seperation clause. I understand that you need to reed this clause in line with your responsibilities.
Firstly, you need to speak with your manager/HR regarding reduced notice period. This period should be a period which must be acceptable to both you and your manager for smooth transition of your responisibilities. Hence, if you are capable to handing over your current responsibilities to your manager within 10 days in a planned manner then the same should be communicated to your manager. Your manager cannot just extend your notice days beyond 10 days due to reasons that he is unable to get a substitute within next 10 days. Your manager can only dispute on grounds that your evaluation of handing over of work within 10 days is stressful for him and hence he may demand 15 or 20 days of time. After the days of notice is negociated between you and your manager, you should write an email to your manager and the HR confirming that you are only serving the number of days as notice period, as has been discussed between you and your manager.
Secondly, you should be ready with the balance pay amount before or at the last day of office.
If you document the above carefully and serve the required number of notice period as decided above, then HR cannot suspend your releving letter. If HR does suspend your releving letter even after you documenting the above process and completing the process of notice pay then you can take-up the issue with the senior management. If you are unable to convince the senior management then you should consult a lawyer to provide a notice to your employer for issuance of your reliving letter. Be careful with all the letters / documents that you exchange between you and your employer on this issue.
RoyS