Air New Zealand aircraft maintenance engineers, aircraft logistics and related staff have scheduled a strike four days out from Christmas.

A new volunteer programme for Qantas' head office workers to spread "a bit of Christmas cheer" at Sydney Airport appears to have had the opposite effect – but Qantas insists the programme is not about cost cutting.

The airline is being accused of "wage theft" and "Grinch" behaviour after an email to staff asking them to volunteer time at the airport during its busiest period was leaked on Friday.

"To support our airport teams at [Sydney International Terminal] over the 2018 peak Christmas travel period, we're trialling a new volunteer program for our Campus-based people who'd like to lend a hand to the frontline in December and January," the email states.

"We require volunteers to assist at the self-service check-ins and auto bag drop area, bussing gates, concourse arrivals hall and at the transfer desk. The roles allocated to volunteers will depend on their preferences, skillset and security requirements."

READ MORE:

* Inside Qantas 787 Dreamliner

* Sydney Airport staff sleeping in third-world conditions at work - union

* Disgruntled Qantas passengers spend New Year's Eve in the sky, dozens more still stranded in Dubai

It's understood that participants in the programme are being asked to volunteer to work shifts of four hours, and are only paid for their time if those shifts fall within their normal rostered working hours.

CAMERON SPENCER/GETTY Qantas' call for head office workers to spread "a bit of Christmas cheer" at Sydney Airport appears to have had the opposite effect.

Australian Services Union NSW branch secretary Natalie Lang said the move amounted to "wage theft" and represents "the classic Grinch tale".

"This is the period where it is so busy that Qantas actually jacks up its prices and price gouges people travelling to see loved ones ... but yet they expect those people supporting those extra travellers to work for free.

"They're robbing everyone at Christmas."

Lang called on Qantas to withdraw the request for volunteers "and instead schedule and pay workers pursuant to their industrial instrument".

A spokesman for Qantas said the programme "is not about cutting costs, this is about spreading a bit of Christmas cheer during a really busy period".

BROOK MITCHELL/GETTY Volunteers would hand out bottles of water and Christmas chocolates to passengers, and help people find their way around the terminal.

"We always scale up with additional paid staff over the peak holiday period," he said. "And we also ask head office employees if they'd like to lend a hand, which is a mix of their own time and company time."

The tasks volunteers are expected to carry out include handing out bottles of water and Christmas chocolates to passengers, and helping people find their way around the terminal, he said.

"It's typically our executives who volunteer, particularly because it's a chance for them to spend more time on the frontline."

But Lang rejected the claim from Qantas that the volunteer shifts are merely an option mostly taken up by salaried executives from head office.

"They would not have this programme if they weren't putting pressure on people to work for free," she said.

"It's offensive to pretend this is about executives walking down to help the front line. If Alan Joyce wants to help, he can go ahead. He doesn't need a programme to do that."