First, be sure which is the appropriate government—whether the Central Government or the State Government—with reference to Sec. 2(a) of the Payment of Gratuity Act, 1972. As per clause (b) of Sec. 2(a), if your establishment has branches in more than one state, then the Central Government is the appropriate government for your establishment, as pointed out by Varghese. Even in the case of the State Government being the appropriate government, the query raised is a relevant one when the establishment has branches across the state. If you carefully go through the contents required to be furnished by the employer in Form A of either the Central Rules or the State Rules, you will find them invariably requiring particulars of both the head office as well as the branches.
At times, the total number of employees in any branch may be less than 10 right from its inception, and also employees may be transferred among the various branches. However, it cannot alter the eligibility of such employees for gratuity. So, my personal view is that the submission of Form A to the Controlling Authority in whose jurisdiction the head office lies would be a sufficient compliance with this rule.
Regards,