Tax deduction at source mandates government entities to withhold GST on high-value supplies, remit timely and enable recipient credit. Section 51 provides for government-mandated tax deduction at source by specified public bodies on supplies above the statutory threshold, excludes deduction where supplier location and place of supply differ from the recipient's registration State or Union territory, treats invoice value net of GST components, requires remittance within ten days after month-end and issuance of a certificate to the deductee, permits the deductee to claim credit in the electronic cash ledger, imposes interest for non-remittance and late fees for failure to issue certificates, and prescribes default determination and refund treatment under the Act.