When a constituent changes credit card information for a sustained gift the credit card is charged $1.00. The notification states the following.
"You can make changes to your credit-card number and expiration date as well as your billing name and address on the following page. After you make your changes, click the Submit Changes button. The system will apply your changes to your next scheduled payment. When you change your credit card information, we will perform a pre-authorization for a small amount, such as $1.00. This authorization may show up on your next billing statement. We appreciate your continued support of our organization."
In most cases the $1.00 is an authorization and not a charge. It is used to verify the card information and in most cases is voided seconds after it is authorized. Note that banks do not have to process the void immediately and so sometimes the void is not processed for a few days. Until that time it may stay on the account as an authorization. In some cases, such as ACH transactions, the authorization must be a charge and in those cases cannot refunded.