No further action was planned but the warning letter would remain on record. It would be taken into account if the trust came to the attention of MPI in the future.
The warning was given in April.
It came to light recently after inquiries by the Horowhenua Chronicle.
The MPI spokesperson said the trust told it that it regretted what happened and had confirmed it would not undertake any further trapping until it had a clear understanding with Horizons Regional Council.
MPI received a letter from the Wildlife Foxton Trust on the same day it received the complaint.
The letter acknowledged the trust was responsible for setting the traps through a volunteer programme and that the obligation to properly service them wasn't met, the spokesperson said.
Wildlife Foxton Trust chairperson John Girling said the trust had been in contact with Horizons and was waiting to hear back if they could resume trapping.
"We are still very concerned about what is happening to our wildlife," he said.