The government says it doesn't know how many jobs could be lost under a plan put forward by NZ Post to cut mail delivery to three days a week.
Communications Minister Amy Adams released a proposal from the national postal service on Tuesday to allow "greater flexibility" in its services to ensure it remains viable as a result of falling mail volumes.
NZ Post wants to change its universal service obligations, signed in 1998, which require it to deliver mail to 95 per cent of locations six days a week.
It wants to reduce the number of mail delivery days to a minimum of three days a week, and introduce more self-service kiosks.
Any changes would require government approval, and the public has a chance to comment on the proposals.
Ms Adams says it's too early to say how many of NZ Post's 7000 staff might lose their jobs under the proposal.
The Engineering, Printing and Manufacturing Union (EPMU) says slashing mail delivery days to three is not sustainable or justified by current mail volumes.
The union is consulting with NZ Post on the proposal.
EPMU postal industry organiser George Collins says the union recognises the commercial pressures NZ Post faces, but it should avoid "kneejerk reactions".
He says the EPMU is working with NZ Post to find a way to adjust while protecting jobs and the post system.
"This may involve a reduction in the number of delivery days or redeployment within NZ Post."
Labour leader David Shearer says it's an unfortunate situation and NZ Post has to make tough decisions, but he hopes it will have a plan in place for staff facing job losses.
He says it's surprising Ms Adams has no detail about potential job losses.
Last April, NZ Post chairman Michael Cullen wrote to State Owned Enterprises Minister Tony Ryall warning that steps to make "fundamental changes to our operational models" needed to take place to cut costs, or delivery days may have to be axed.