What action must a firm take when receiving cash in excess of $10,000 from a single customer in one business day?

When a firm receives cash in excess of $10,000 from a single customer in one business day, it is required to file a Currency Transaction Report (CTR). This requirement is part of the regulations established by the Bank Secrecy Act, which aims to combat money laundering and other financial crimes. The CTR must be filed with the Financial Crimes Enforcement Network (FinCEN) and should include details about the transaction, the individual or entity involved, and the source of the funds.

Filing a CTR is crucial because it provides insights into large cash transactions, which may indicate suspicious activities that could be related to illegal actions. The threshold of $10,000 is set to ensure that large cash activities are monitored and reported, helping regulatory agencies track and prevent potential money laundering schemes.

The other options do not fulfill regulatory requirements related to large cash transactions. While notifying the Securities and Exchange Commission or transferring funds to a separate account might be relevant in other contexts, they do not address the specific legal obligation to report large cash transactions. Additionally, limiting future transactions doesn't comply with the proper regulatory procedure and does not account for the requirement of transparency that the CTR serves.