A credit union must file a CTR if a member purchases $15,000 worth of traveler's checks with money from their checking account.

A credit union is required to file a Currency Transaction Report (CTR) when a member engages in a transaction involving cash that exceeds $10,000. However, in the case of purchasing traveler's checks using funds from a checking account, the transaction does not involve cash. Instead, the member is using electronic funds from their account to make the purchase. Therefore, the transaction does not trigger the requirement to file a CTR, as there is no cash physical exchanged in the process.

It is important to understand that CTR requirements are specifically focused on cash transactions. Cash here refers to physical currency, and transactions being conducted solely through bank accounts or checks do not meet the criteria. Thus, the correct interpretation is that the credit union would not need to file a CTR for the purchase since the transaction is made using funds from a checking account and does not involve any cash.