That forgotten library book might just show up to blot your credit history.

With a million dollars in overdue and lost charges at Wellington libraries, many are referring members to debt collectors and credit rating agencies.

Wellington, Hutt City and Upper Hutt libraries passed more than 2400 members to collectors in recent years, with many getting a mark on their credit history, a Local Government Official Information and Meetings Act request showed.

Wendy Lane, of Lower Hutt, said such policies were heavy-handed for a community service.

Her daughter Jessica Kaczorowski, 12 at the time, was threatened with debt collectors last year after books and a DVD mistakenly unreturned for about a month racked up $300 in late fees at the Lower Hutt branch. "It was just wrong six ways to Sunday . . . Normally the people who are getting to that debt collection stage are of lower socio-economic status and, funnily enough, are the people who need the library the most."

The letter addressed to Jessica on debt collection proceedings was the first time Lane, who had been ill, realised there was an issue. Librarians told her that warning emails had been sent, but these went to a spam folder.

While she paid, Lane thought the fines were excessive. "Where does it go from being a way of getting books returned to a way of increasing your revenue?"

Hutt City Libraries manager Sandra Mann said it was "not always ideal" to charge overdue fees, and patrons could sign up for reminders. "We just want the items back so they can continue to circulate and be of use to others."

The council required branches to charge overdue fees to help pay for services, she said.

Wellington City Libraries manager John Stears said 10 per cent of operating costs came from user fees. "We do all we can to recover outstanding amounts."

Wellington libraries waived fines if ill health, bereavement or similar issues were the cause, and were happy to work with members on payment plans, if they reached their $80 threshold for debt collection.

Upper Hutt libraries also worked closely with patrons owing items and fees, council community services manager Debbie Duncan said. "We have a responsibility to our ratepayers . . . Any referral to debt collection services is an extremely last resort."

Debt collectors either charge a commission on collected debts or purchased them and kept the recovered money.

Porirua branches operated an item-only recovery system. An automatic scheme triggered when a member had items worth more than $90 still unreturned six weeks after their due date, library manager Bryan Anderson said.

Kapiti Coast branches do not use debt collectors or credit agencies.