Credit unions are not obligated to honor postmark dates when considering timeliness of a payment. The credit union considers the date when the payment was received—not when it was mailed.
Please keep in mind that your payment must be mailed in enough time for the credit union to receive it on or before the due date.
Beginning February 22, 2010, if the payment due date falls on a day when the credit union does not accept or receive postal mail, your mailed payment is considered timely if the credit union receives it by the cut-off time on the next business day. For example, if your due date falls on a federal holiday when the credit union does not receive mail, you generally have until the cut-off time on the following business day to make a timely payment by mail.