It was sent 45 minutes early, the RBNZ said.
"The limited information contained in the letter is unlikely to have provided anyone with a market advantage, but the Reserve Bank is taking the matter seriously."
"The Reserve Bank is working closely with the reviewers, and will comment further on any outcomes when the review is complete."
Funding for Lending (FLP) is a mechanism for the RBNZ to lend some of its freshly printed cash directly to commercial banks at special rates - as opposed to just providing a wholesale lending facility (which it does with its Official Cash Rate).
FLP would effectively offer commercial banks a discounted retail rate which would lower their funding costs and enable them to cut mortgage rates further.
In its announcement last Wednesday no details of the scheme were released, with the announcement confirming it would begin in December.
Detail about the scheme are expected in coming days.
The disclosure breach comes four-and-a-half years after the Reserve Bank abolished media "lock-ups" for the OCR announcement because TV3 broke an embargo.