"This may involve a reduction in the number of delivery days or redeployment within New Zealand Post, but we would caution against any kneejerk reactions."
Mr Collins said EPMU also had concerns around the "integrity" of New Zealand's postal service.
"Are New Zealanders going to wait days for their mail?"
He said the union was under no illusions about the financial realities of the situation, but it was about finding a long-term solution that was sustainable for everyone.
Communications Minister Amy Adams and NZ Post say it's too early to tell how many of the 7000 postal employees will lose their jobs should a proposal to cut mail delivery services to three days a week go ahead.
The move was first suggested by former NZ Post chairman Jim Bolger three years ago in response to diving letter volumes associated with the rise of email over the last two decades. That decline has accelerated sharply in recent years.
The proposal would require changes to Universal Service Obligations - an agreement between NZ Post and the Government which guarantees postal services to the public.
NZ Post will also consult on proposals to bring self-service kiosks for some services.
"New Zealand Post has advised me that it considers changes are needed to ensure a sustainable postal service in the 21st century," said Ms Adams.
"Any change would require Government approval, and before deciding what, if any, changes to make, I want to give the public the opportunity to comment on the proposals.
"We want them to start thinking about the last time that they got a letter that was so time sensitive that another day would make a difference. It will be a big change, a significant change and that's why we need to have a good conversation with the public."
Spokesman John Tulloch said the electronic kiosks would provide a number of services from wiring parcels to paying bills.
NZ Post was trialling kiosks in 10 stores, but they weren't necessarily the models that would be used.
"What we're looking at doing is putting more of that technology into the network to extend that presence."
While the prospect of an entirely kiosk-driven model wasn't likely soon, it was a possibility in the long run, he said.
"We're still very beholden to the traditional model."
The proposal also "takes account of the fact that technology and changing customer behaviours mean services can and will be provided through various channels," Mr Tulloch said.
Long-term, this could mean the extension of services to supermarkets, stationery stores, pharmacies and service stations.
NZ Post employs about 7000 staff in its mail division including about 2200 posties.
Ms Adams told reporters that job losses were "something that they'll be talking to their posties about".
"What they will have to look at is how they will provide that service whether they use the same posties doing different routes on different days. That's something they will work through."
