"Unfortunately, technology is dramatically changing the way we communicate with each other ... at the same time we're seeing an increase in jobs in the IT space.
"It's a change that not just New Zealand but a lot of other countries are going through."
Mr Key disagreed with the union that the Government had made the announcement "out of the blue".
"There's been a lot of discussion about what would happen if there was a change to the number of days that the mail was delivered to people's homes.
"Overall, I think this has been well and truly telegraphed."
Engineering, Printing and Manufacturing Union postal industry organiser Joe Gallagher said the announcement had come as a shock to members
"Yet again New Zealand Post and the Government have made a huge announcement out of the blue.
"These plans have clearly been in the pipeline for a long time, but the people affected by them, including all New Zealanders who use the postal service, have been kept in the dark."
The company's plans include:
• Giving customers the choice of a priority overnight delivery and non-priority service.
• Getting posties off bikes and into vehicles.
• Closing specialist Post Shops and putting them in another business.
• Post will now be delivered at least three days a week in towns and cities and five days a week for rural addresses. There will still be a "premium service" six days a week.