The invention provides a method and system for blocking fraudulent or incorrect Automated Clearing House (ACH) debits. In an embodiment of the invention, the number of fraudulent and incorrect ACH debits is significantly reduced by examining an ACH debit entry and determining if it is identified as a consumer-oriented transaction directed to a commercial account. Particularly, a number of computer programs is provided at a Receiving Depository Financial Institution (RDFI) to automatically return ACH debits to the Originating Depository Financial Institution (ODFI) via the ACH Operator if the standard entry code (SEC) identifies the transaction as a consumer oriented transaction and the paying account, i.e., Receiver, as a commercial account. Consumer ACH debits can be posted to a commercial account, however an immediate and automatic credit in an amount equal to the debit is applied to negate the debit. Within 24 hours, a message is returned to the Originator's ODFI specifying that the debit is unauthorized, thereby providing an audit trail of the unauthorized debit for all involved parties in the ACH network.