It applies to the merchant who plans to convert the customer's check to an ACH item. Your disclosure obligation relating to check conversions is in making sure your account disclosures list ACH transfers initiated by converting the customer's check as a form of EFT that can affect the customer's account.
Of course, if your institution converts checks it receives to ACH entries (loan and mortgage payments, credit card payments, etc.), you'd put yourselves in the place of the merchant, and have to use the model language in Model Clause A-6 (and possibly A-8).
John S. Burnett
Fighting for Compliance since 1976
Bankers' Threads User #8