The Department of Conservation says some trampers are putting themselves in danger by camping illegally to avoid paying to walk the country's most popular tracks.
DOC said It was a nationwide problem, but was worst on the Milford, Routeburn and Kepler Tracks in the South Island.
Its Queenstown partnerships ranger, Chris Hankin, said the campers were damaging the fragile environments which the tracks cross.
"Just the impacts get greater and greater and you end up with quite messy campsites and some of them I have seen rubbish left behind and they leave fires where they shouldn't. The great walks are beautiful walks and they are really popular and we want to keep them that way as great walks."
Mr Hankin said they trampers were putting themselves at risk as the terrain away from the tracks was often dangerous and DOC didn't know they were in the area.
He also said trampers going off the tracks were missing out on any weather warnings provided by hut wardens.