What you need to know about Point-of-Purchase (POP) entries
A Point-of-Purchase entry is an application of the automated clearing house (ACH) network, the same network that allows for Direct Deposit. When you present a check to a merchant in payment for goods or services, for ease of handling they may convert your check to an ACH entry. The merchant will scan the check to obtain your banking information from it, then void the check and return it to you. Once they've voided the check, you must not re-use it. Treat it like you would any voided check.
Prior to transmitting a POP entry, the merchant is required to obtain your approval by having you sign a written authorization and then providing you with a copy of it. The authorization permits them to inititate a one-time debit to your bank account for the amount of the purchase. (If the original debit is returned due to insufficient funds, the merchant may re-initiate this debit via the ACH. The authorization you signed may include language allowing the merchant to assess a 'collection fee' to you if your payment is returned.)
These ACH entries will be listed with the electronic transactions on your statement and will contain the check number of the voided check and the purchase amount to help you identify the transaction. You may place a stop payment on an ACH entry but, since this entry could reach your bank by the next day, you must act quickly. Immediately contact your financial institution and tell them you wish to place a stop payment on a "Point-of-Purchase" transaction. Be sure to have the check number, transaction amount, and the date of the transaction ready.