What action should a cardholder take regarding fraudulent transactions?

The most appropriate action for a cardholder regarding fraudulent transactions is to contact the US Bank fraud department. This step is essential because the fraud department specializes in handling such incidents. They have the resources and expertise to investigate the fraudulent activity, help secure the account, and prevent further unauthorized transactions.

Additionally, contacting the fraud department ensures that the cardholder’s report is documented and managed according to the bank's protocols. This communication helps to protect the cardholder's financial interests and provides a formal avenue for resolving the situation.

While other actions, such as reporting to a supervisor or canceling the card, may seem reasonable, they do not directly address the immediate need to secure the account against fraud. Reporting to a supervisor may not lead to prompt action, and canceling the card does not provide a means to address the fraudulent activity already occurring. Furthermore, doing nothing until a large amount is involved is risky, as any unauthorized transaction should be addressed immediately, regardless of the amount involved.