The beach and dunes more than 200m south of the Department of Conservation (DOC) campground at Uretiti have long been a safe haven for people who prefer an all-over tan.
But some men have been walking naked along the southern boundary of the campground or stripping off in the public day area north of it.
Campground manager Kevin McCleary said naked men had been found watching young girls or swimming near children on the beach in front of the campground.
Police were called last month after a woman complained about a man behaving indecently after he crept close to her when she was sunbathing nude.
Ruakaka police yesterday confirmed the 32-year-old man had not been charged because the woman had not wanted to take the issue to court.
The Uretiti campground is DOC's largest, with up to 500 sites.
Mr McCleary said he wanted visitors to enjoy the beach without naked men causing offence.
"My biggest concern is that someone like a child's father could take the law into their own hands,'' he said. "I'd like people to respect Uretiti is a public beach and any form of nudity in the campground reserve or on the beach in front of it is unacceptable.''
Mr McCleary said that when he asked a man who was naked on a walkway by the camp to put on his pants, the man said he had a right to be nude at Uretiti.
"I warned him I would call the police if he did it again. There are no legal nude beaches in New Zealand,'' Mr McCleary said.
He quoted a 1981 law on indecent exposure that warned a person faces up to three months in jail or a fine of up to $2000 if they ``intentionally and obscenely expose any part of his or her genitals'' in or within view of any public place.
People can defend themselves against prosecution by proving they have reasonable grounds for believing they would not be observed.
Mr McCleary said there were no official signs at Uretiti advising where people may be unclothed because nudity was illegal.
He suggested nudists should put up a marker defining the area south of the camp where clothing was optional.
The beach's reputation for tolerance toward nudity began years ago when naturist members of the Motor Home Association started staying there.
Mr McCleary said naturists valued privacy and disliked exhibitionist behaviour around the camp.
New Zealand Naturist Federation (NZNF) president Pete Whalan said his organisation did not support such behaviour and he doubted the men involved would have been NZNF members.
"People that do these things and behave like that is a concern to us, because our members are well aware of their rights as far as swimming nude.''
He said there was no law that prohibited public nudity.
"There's a distinct difference between public nudity and offensive or lewd behaviour, we all have the right to go to the beach and enjoy the beach and swim naked, and sunbath naked.''
It was people like these men who tarnished their group's reputation, he said.
"It appears these people have been naked on pathways and the like, which is not illegal, but it's not appropriate, they should be in the area where it's accepted they go.''
Up to 800 people are expected to be at the Uretiti campground for New Year's Eve.
There had been mayhem on New Year's Eve in the past, but new security measures should ensure campers see in 2012 without disruption from alcohol-fuelled revellers wanting to party at the beach.
The public day area by the campground will be closed from 9pm on Friday and the main gates to the campground on State Highway 1 will be closed from noon on Saturday.