A surge in people abusing staff, causing fights and stealing property has forced the Rotorua Library to introduce strict new security rules, including taking out trespass notices against troublemakers.
The move comes as the library's director admits it had become a "soft spot" for thieves, some of whom were targeting tourists.
Jane Gilbert said trouble had increased since the library introduced free wi-fi last November.
"Initially it all went well, but around July/August we started to get people coming in and targeting tourists. It was like people suddenly realised it was a soft spot for pinching things," she said.
Mrs Gilbert said the wi-fi had made the library busier which helped the thieves blend in.
I've been working here 26 years and it's the worst I have ever seen it. In the last month we have had four thefts that I know of.
"It's sad, but we have had to trespass people."
She said staff had to call police to deal with people abusing staff, causing fights, or skipping school to hang out in the library.
However it was often hard to identify the offenders on the library surveillance cameras because they were wearing hats or other things that covered their faces, she said.
Mrs Gilbert said Inspector Bruce Horne from the Rotorua police had worked with library staff on security.
"We had received complaints, not only from the library but from people who like to go there," Mr Horne said.
"Crime is all about opportunity, we just have to minimise the opportunities."
At Mr Horne's suggestion, a sign was put up at the library entrance asking people to take off their headgear, hats, hoodies, sunglasses or anything else that might obscure their faces.
"Initially people weren't happy, but now they are being co-operative. It's just something that we have to deal with. If we don't do anything then the atmosphere will disappear, and we don't want that," Mrs Gilbert said.
She said anyone with a medical condition or a cultural belief that required them to wear something on their head should have a quiet word with one of the staff members when they entered and an exception would be made.
She said they were currently looking to make a secure space where people could place their belongings.
Rosemary MacKenzie told the Rotorua Daily Post her husband was asked over the loudspeaker to take off his hat and glasses.
Mrs MacKenzie said her husband had a medical condition that required him to wear a hat and transition lenses indoors.
"If we had had a staff member come over and tell us quietly it would have been a different story, but to have it said over the loudspeaker and everyone turn and look was wrong."
Mrs Gilbert said she had received Mrs MacKenzie's complaint and had replied with an explanation of what the library was trying to do.
"We are also putting things over the intercom to help people understand what is happening,"she said.