Any manufacturing company has to inform the government authorities about the following:
1. Change in the timing of any shifts
2. Addition/deletion of any shifts
3. Change in weekly holidays
4. Changes in extra working days
5. List of paid holidays issued for the current year.
In your case, no permission needs to be taken, but I suggest that you should issue a circular with a CC to the Labour Commissioner, stating the change or addition of the second shift in your company. This circular can be sent to the Labour Commissioner just to inform them. This will prevent you from receiving any negative remarks during the visit of the Factory Inspector.
Regards