Compulsory registration for specified suppliers under GST: several categories including inter state, casual, reverse charge and e commerce operators must register. Compulsory registration is mandated for specified persons including those making inter-State supplies, casual taxable persons, persons liable under the reverse charge mechanism, persons liable under the specific charge provision of section 9(5), non-resident taxable persons, tax deductors, agents supplying on behalf of others, Input Service Distributors, electronic commerce operators and suppliers through e-commerce operators, and persons supplying online information and database access from outside India to unregistered recipients; additional classes may be notified.