Dear Balaji,
Legally, we cannot hold anyone to avail their leave during the Notice Period. However, one can be stopped by adding the following paragraph in the appointment letter:
"In the event of resignation after confirmation, you will have to serve the full notice period to facilitate a smooth transition. The notice period cannot be adjusted for unavailed leave. In exceptional circumstances only, and with the specific approval of the competent authority or their nominee, one may be permitted to pay the company an amount equivalent to the gross salary in lieu of notice. Failing which, the resignation will not be accepted, and the same will be treated as abandonment of service."
Regards,
Deepak Agarwal