Gst registration

A service provider has his place of business in 3 states (including Delhi where the Head office is situated) he follows a system of centralized billing from Delhi office and no invoices are raised (i.e. no services are provided) from the other 2 branches. Presently he has centralized registration under Service tax. Is the service provider required to obtain registration under GST in the other 2 states even though there is no supply from those branches and no invoicing is done from those branches ?