Banks in the United States are required to report cash deposits in excess of $10,000 to the IRS. The requirement pertains not only to one lump sum cash deposit in excess of $10,000 but also to two or more related deposits that total over $10,000.
Related transactions are those that occur within a 24-hour time period. In addition, if a bank reasonably believes that a series of cash deposits are related, even if they are made outside of the 24-hour time frame, the IRS reporting is triggered. The primary underlying purpose behind this reporting requirement is to combat illegal money laundering and related types of fraudulent conduct.