Union officials have criticised Chorus's business model after it made changes that could see up to 25 Downer employees lose their jobs.

Downer will no longer look after ultra-fast broadband (UFB) installations in Manawatu, Wellington and Kapiti Coast after Chorus switched the contract to Visionstream this month.

E Tu Union telecommunications industry co-ordinator Joe Gallagher said this would likely result in Downer having to cut 25 roles in the lower North Island - 11 in Palmerston North and Manawatu District and 14 in Horowhenua, Kapiti Coast and Wellington.

An unknown number of subcontracting jobs would also be lost, he said.

Downer was unable to confirm the number of jobs being cut but company spokeswoman Brooke Dahlberg said they were working closely with Chorus to provide options for the affected workers.

Workers could have the chance to either move to Visionstream or remain with Downer and continue to work on the copper network, she said.

Gallagher said the business model now being used by Chorus was unfair to workers and unsustainable.

He said most of the former Downer workers would move to Visionstream, so it could effectively be the same people doing the installations.

​"How is that going to enhance the outcomes? In my opinion, it's just about saving some money for Chorus."

Gallagher said Downer paid installers a salary, while Visionstream worked on an owner/operator model that gave them a share of the profit.

"I don't think it's a sustainable model; our concern is that all the risk is being transferred to the workers."

Chorus customer services manager Nick Woodward said demand for fibre was increasing significantly, and more technicians would need to be recruited than would be affected by the change.

"We have had such a high demand for fibre in the Wellington region that we need to make changes to ensure consumers are connected to fibre much quicker than is currently the case,"

Visionstream starts work on UFB installations in Wellington and the Kapiti Coast on May 16, and in Manawatu on May 30.

It took over Chorus's installations from Downer in Porirua in November after customers complained about how long it was taking to be connected to high-speed internet.

Chorus spokesman Nathan Beaumont told Stuff at the time that the changeover had immediately improved waiting times.

"Since Visionstream took over fibre installs in Porirua from Downer late last year, the time it takes to get the first appointment for a fibre install has reduced from 24 days to four days, so massive improvement. The average across the country is about 17 days."

Beaumont said feedback indicated Visionstream workers really liked the model, and it had a good track record of attracting new crews and getting through jobs quickly.

"[It's part of] establishing the right environment that will support technicians to be most productive and have a sustainable living, and to cater to the increasing trend of workers to be self-employed by choice or have more flexible working conditions."

​Visionstream also conducts UFB installations in Auckland, and could be given other areas in the future.

Downer retains the contract to connect customers to UFB in Napier, Hawke's Bay, Gisborne and the South Island. It also manages Chorus's copper network in the lower North Island and lower South Island.