OFAC Blocking Obligation

The legal requirement to freeze assets when a sanctions match is identified in the middle of a transaction.

TL;DR

TL;DR: When a counterparty matches the SDN List, US persons must block the funds, not merely reject the transaction, and must report the blocked property to OFAC.

Blocking versus rejecting

Blocking means property is frozen in place, placed into a blocked account, and reported to OFAC. Rejecting means the transaction is simply not completed and the funds are returned. The distinction matters because a match against the SDN List triggers the blocking obligation, while other list matches may only require rejection. Acting on the wrong one can itself create an enforcement problem. Blocked property also carries a reporting duty: the holder must file a blocked property report within 10 days and an annual report by September 30.

When the obligation triggers

The obligation attaches at the moment a sanctions match is identified. Because OFAC applies strict liability, intent is not required: a payment that slips through to a blocked party is a violation even if no one noticed the match. This is why screening must happen before funds move, not after settlement.

Blocking in agent payment flows

sanctionsai.dev encodes this decision as a clean binary. The agent sends a screening request before paying; a clean counterparty returns ALLOW, and a flagged counterparty returns BLOCK. Under the 4-Gate Agent Payment Protocol, SCREEN, SCORE, STOP, and STAMP, the STOP gate halts the payment so the blocking obligation is honored before value transfers. For most payment systems, the practical answer is to stop the transfer the instant a match appears, before blocking is ever necessary.