There are no laws or regulations that specify when you should check for OFAC-specified customers. Instead, there are penalties for failing to block, reject, or report a transaction with an OFAC-specified country, entity, or individual. See Economic Sanctions Enforcement Guidelines, Appendix A to 31 CFR Part 501 (under which a bank’s OFAC compliance program can mitigate the penalties imposed for violations, with consideration of the views of the bank’s regulators). 

According to the FFIEC’s most recent Bank Secrecy Act/Anti-Money Laundering Examination Manual, your review frequency “should be based on the bank’s OFAC risk. For example, banks with a lower OFAC risk level may periodically (e.g., monthly or quarterly) compare the customer base against the OFAC list. Transactions such as funds transfers, letters of credit, and noncustomer transactions should be checked against OFAC lists prior to being executed.” Office of Foreign Assets Control — Overview. 

OFAC also provides a compliance hotline for banks to use for various purposes, including clarification on OFAC regulations: (202) 622-2490/(800) 540-6322; [email protected].