Which situation would result in a credit card issuer charging a balance-transfer fee?

A credit card issuer would charge a balance-transfer fee when a cardholder transfers an existing balance from another credit card to their card. This fee is typically a percentage of the transferred amount or a flat fee, depending on the issuer's terms. The fee compensates the issuer for processing the transfer and assuming the risk associated with the new balance. It's important for cardholders to review the terms before initiating a balance transfer to understand any associated costs.