NACHA is the membership association that maintains the *NACHA Operating Rules* — the rulebook for US ACH credit and debit transactions. Both ACH operators (FedACH and The Clearing House EPN) clear and settle ACH entries under the NACHA rules.
NACHA defines the SEC codes (PPD for consumer credits/debits, CCD for corporate, WEB for internet-initiated debits, TEL for telephone-initiated debits, IAT for international ACH) and the corresponding addenda-record requirements.
The "NACHA file" is the customer-bank transport format — fixed-width 94-character records. The customer's bank takes the NACHA file and submits to the operator on the customer's behalf.
iso-compliant does not produce NACHA files. The Phase-3 plan is to map pain.008 / pain.001 onto the equivalent NACHA SEC codes for tenants that want a single corporate-bank message format that fans out to US ACH plus SEPA SDD / SCT under the same code path.