Cadbury is reducing the size of its blocks of chocolate for the second time in four years.
The company said its costs were increasing and it either had to raise the price or cut the size.
Most of the blocks will be about ten percent smaller, changing from 200 grams to 180.
Cadbury marketing director Paul Chatfield said the company was conscious of cost pressures facing New Zealand households, so it chose not to increase the price.
"We recognise some Cadbury fans will be disappointed by the smaller block size, so we're working with our retail partners to ensure we continue to deliver the best value to consumers," Mr Chatfield said.
He said the company would talk to retailers about reducing the recommended retail price about five percent, from $3.79 to $3.60.
The company acknowledged it could not control whether or not shops would drop their prices.
When the change takes place most blocks will be more than 20 percent smaller than they were in 2015, when a similar change was made.
That change, almost four years to the day, was also done "in an effort to ease the pressure of rising costs".
The size reduction will also take effect in Australia.