Compulsory registration expands GST obligations to inter state, casual, non resident suppliers and e commerce operators. Compulsory registration applies notwithstanding general registration thresholds to specified categories: persons making inter state taxable supplies; casual and non resident taxable persons; persons required to pay tax under reverse charge or other specified tax provisions; persons supplying on behalf of others including agents; persons required to deduct tax at source; Input Service Distributors; every electronic commerce operator; and suppliers of online information and database access or retrieval services from outside the country to unregistered recipients. The government may notify additional classes of persons.