A staff information document, Fit for the Future, issued last August and obtained by the Herald, said there was a need to cut staffing by about 5 per cent.
Part of the reason for Fit for the Future is to make "significant savings" as part of an organisation-wide efficiency drive. The library budget is $65 million, of which staff costs make up two-thirds.
In his letter, Trussell said it was difficult to see how fewer roles could meet the city's growing population if the ranks of the staff were thinned and then spread out across more libraries.
"Fit for the Future, in light of all this, might be better entitled Unfit for the Future," wrote Trussell.
He said library staff, who are among the lowest-paid council workers, do more than just issues books, CDs and videos "they are essential in making knowledge available to all age groups".
"This they do graciously and with alacrity. They are the lifeblood of institutions that are our 'information commons'," said Trussell.
Cost-cutting, he said, was a lose-lose strategy, not minor and "to the best of our knowledge, no public submissions have been invited".
Documents obtained by the Herald under the Official Information Act show that Fit for the Future is designed to reflect on the growing and changing needs of libraries to ensure the services remain contemporary, best practice and able to adapt to change.
Proposals include making staff work move around libraries and increasing their skills to work in new ways.
"Separate, but occurring in a parallel time frame, we are also identifying opportunity to reduce costs whilst maintaining levels of service," chief operating officer Dean Kimpton said in an email dated last November 10.
Details about reduced staff numbers and costs have been redacted from a Fit for the Future business case.
The plan is not to reduce opening hours or close libraries, but a response to fewer, but longer, visits and more electronic checkouts. In the past year, library visits have reduced from about 12.5 million to 12m. Five years ago, there were nearly 14m visits.
A council spokeswoman said managers are reviewing the proposal this week and will meet all library staff at a series of meetings next week.
Staff will have until mid-February to provide feedback on the proposal.
The spokeswoman said Edmundson had responded to Trussell on December 22 via the society's secretary and offered to discuss his concerns in the new year.
Trussell todaysaid he had not seen a copy of the response.