TDS under Section 51 requires specified government-controlled entities and public undertakings to deduct tax on supplier payments. Appointment of the commencement date for Section 51 imposes withholding obligations on specified authorities, government-established bodies, societies registered under the Societies Registration Act, and public sector undertakings to deduct tax at source from payments to suppliers of taxable goods or services, with the effective date for some categories to be notified subsequently on the GST Council's recommendation.