Explanation/Reference: https://www.acams.org/aml-resources/eu-fourth-aml-directive/

A subpoena is a legal order that requires a person or an entity to produce documents, information, or testimony related to a legal matter. A financial intelligence unit (FIU) is a specialized unit within a financial institution that is responsible for detecting, analyzing, and reporting suspicious activities and transactions. When a bank receives a subpoena regarding one of its clients, the FIU should review the subpoena and perform a transaction review to determine if there is any evidence of money laundering, terrorist financing, fraud, or other criminal activity involving the client. The FIU should also respond fully to the subpoena by providing the requested information and documents, unless there is a valid reason to object or seek a protective order. The FIU should not adjust the client's risk score, file a SAR, or close the client's account based solely on the receipt of the subpoena, as these actions may be premature, inappropriate, or illegal. Adjusting the client's risk score may require further investigation and due diligence. Filing a SAR may be unnecessary or misleading if the subpoena does not indicate any suspicious activity. Closing the client's account may violate the bank's contractual obligations, customer service standards, or anti-discrimination laws. Moreover, these actions may alert the client or the subject of the investigation to the existence of the subpoena, which may interfere with the legal process or jeopardize the safety of the bank or its employees.
References:
Subpoena Responses for Financial Institutions
Requests by Law Enforcement for Financial Institutions to Maintain Accounts SUBPOENA COMPLIANCE UPDATE
[ACAMS Study Guide, 6th Edition, Chapter 5, p. 140]