A Waitakere Township resident has a warning for locals after a threatening letter was left on her car window while she was parked outside Waitakere Primary School.

On Tuesday the resident went to park down Anzac Valley Rd so she could watch the school's cross country.

But when returning to her car, which she claims was parked on the gravel near the school, she found a nasty note on her windscreen.

The person behind the note takes aim at the driver of the car, threatening to lay down nails should the driver return.

The note reads: "Please don't park on my grass as it causes damage to the berm. Which makes it extremely difficult to mow.

"As from tomorrow there will be nails placed so that the next time you decide to park here you are more than likely going to get a flat tyre.

"If you were polite enough to knock and ask if I minded you parking here, you would have been told NO!

"I don't care if you have nowhere else to park, not my problem. Next time I won't be so polite, as I will treat you with the same disregard as you are showing me."

The person behind the note threatens to place nails in the grass. Photo / Facebook

The resident posted the letter to a local community Facebook group in a bid to warn others about the threat.

Members of the community have since hit out following the note, warning their actions could harm children walking home from school.

"I hope no kids walking home from school stand on nails," one person wrote.

Another local claims there have been a few run-ins with the alleged note writer.

One joked: "Good luck to them mowing their laws with nails all through it.

The NZTA road code says you may "park the vehicle off the road without damaging grass or gardens (a controlling authority may have a bylaw and/or signs prohibiting parking on a grass verge)".