Compulsory registration requirement expands taxable persons to include inter state suppliers and specified electronic commerce operators. Section 24 mandates compulsory registration for specified categories notwithstanding section 22, including inter State suppliers, casual and non resident taxable persons, persons liable under reverse charge, persons under sub section (5) of section 9, tax deductors under section 51, agents making supplies on behalf of others, Input Service Distributors, electronic commerce operators and suppliers of online information and database access or retrieval services from outside India to unregistered persons in India, and permits the Government to notify additional classes for registration.