Auckland Council is standing by its decision to shed library staff, but a union is disappointed it's being used to help justify the decision.

The council has formally rejected a petition signed by 3500 people, asking it to reconsider cutting more than 70 roles at the council's libraries department.

In a letter to petition organiser Julia Schiller, chief operating officer Dean Kimpton said the decision had the support of the Public Service Association, the union representing library workers.

"I have reviewed the petition, discussed the matter with senior library staff, and looked at feedback collected from staff during the consultation process.

"From early on, the [union] has contributed to its design and supports the process we have adopted."

But union national secretary Glenn Barclay has confirmed to Newstalk ZB the PSA never supported the restructure, and had only been representing members through the council's process.

"We're disappointed that the council has said that the PSA supports the process.

"They've made the statement without consulting us, and we don't think that that's an accurate representation of our involvement."

He said the union has been "advocating strongly for members" through a constructive but robust negotiation process with the council.

"You don't achieve anything just throwing stones through the window. You need to be involved through the process."

The petition has gained a further 900 signatories since Schiller presented it to the council at the end of last month, bringing the total number of signatories to 4400.

She told the council she wanted to know why a controversial restructure and hiring freeze had been started shortly before last year's council elections, rather than being voted on by the new council.

The council has previously said the restructure will save the council $1.8 million a year, and there will be enough roles for every staff member who wants to keep working at the libraries.

Auckland Council libraries manager Mirla Edmundson said there will also be no reduction to library opening hours or services.

"Our 55 community libraries, along with our research and heritage services and our central library, will still be continuing to offer the same opening hours and high-quality experience."

She said some jobs were being cut, to create new mobile, digital, online and call centre roles, to serve Auckland's "socially and geographically isolated communities".