Tax Deduction at Source under GST mandates notified deductors to withhold tax on large contracts with deposit and reporting duties. Section 51 mandates Tax Deduction at Source by specified government and notified persons on contract supplies exceeding the prescribed threshold (contract value excluding GST). Applicability depends on supplier, place of supply and recipient locations; exceptions arise where both supplier and place of supply differ from the recipient's State/UT. Deductors must register, deposit withheld tax by the tenth of the succeeding month, issue Form GSTR 7A within five days, file Form GSTR 7 monthly, and the credited amounts reflect in the supplier's electronic cash ledger; specified interest and late fees apply for non compliance.