Compulsory registration required for specified suppliers including inter state, casual, non resident, reverse charge and ecommerce operators. Compulsory registration applies to persons making inter State supplies, casual and non resident taxable persons, those required to pay tax under reverse charge or other specified provisions, persons required to deduct tax, agents or persons supplying on behalf of others, Input Service Distributors, electronic commerce operators and suppliers of online information and database services from outside India to unregistered recipients; the Government may notify additional persons or classes for mandatory registration.