The scrapping of nearly one million book loans to schools each year will let down students who are not prepared for digital alternatives, the Labour Party says.
The National Library will this year stop one of its services to schools in favour of providing more online resources.
Internal Affairs Minister Peter Dunne says the changes will go ahead as scheduled, despite strong opposition from several teachers and the School Library Association.
"This is really about making more resources available ... I think once it is all in place people will wonder what all the fuss was about," he said.
Labour has fielded concerns from several schools and teachers about the change. MP Jacinda Ardern disagreed with Mr Dunne's claim that schools would not be greatly affected because they could access improved electronic resources.
"There will certainly come a time when this service may be overtaken by other ways to access resources.
"But right now, we cannot guarantee there is equal digital access across all our schools. Particularly if you are rural or a smaller school."
A long-standing service has enabled teachers and school librarians to contact the National Library and request copies of non-fiction books on a specific topic. A librarian at the National Library then sends a box of appropriate books to be used in class. About a third of all teachers use the service, with nearly one million book loans each year.
But from term three this year, the scheme is to be scrapped as part of an overhaul of the National Library's service to schools.
National Librarian Bill Macnaught said the library would continue to build its book collection for use by schools. Its librarians would send a collection of books to schools, selected to encourage students to read for pleasure.
To help teachers on a specific topic, a selection of online resources would be strengthened.
Mr Macnaught said teachers who wanted hard copies of a specific book would be able to borrow them from the National Library, through a request sent by the school library.
Targeted support would be provided to low-decile and other priority schools.
Timing for the changes, which came after an independent review commissioned by the Department of Internal Affairs, was "tricky", he said.
It was not realistic to offer the current service as well as growing online resources, particularly if the National Library was to address a concern raised in the review that access to its services was uneven.
"Given the diversity of curriculum topics, the only way we can get resources into schools in an equitable basis would really be by using ... digital [options]."
But School Library Association president Bridget Schaumann said some schools would be hit hard. "These books exist, they are well used ... it just seems like a terrible waste."
• The National Library will this year stop allowing teachers and school librarians to request non-fiction books on a particular topic.
• Online resources to be expanded as an alternative, and a range of books will be sent to each school to encourage reading for pleasure.