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The business was started by James Henry Whittaker in Christchurch in 1896 and was later moved to Wellington.
A statement posted to the company's social media channels on Monday morning suggested it was necessary to increase the prices to maintain quality standards.
"We wanted you to be first to know that from today we will unfortunately be bringing in a price increase," the social media post said.
"This is something we have resisted for the last two years, but over that time our costs have steadily risen. Cutting those costs with lesser quality ingredients is never an option for us, as we hope you'll understand."
Whittaker's last increased the price of its chocolate bars in 2019, also in response to rising production costs.
The latest price increase comes amid growing concerns about the level of inflation in New Zealand.
Inflation data released in July showed the Consumer Price Index was up 3.3 per cent year-on-year.
This was the biggest increase in nearly 10 years and was driven by higher prices for new housing and petrol, StatsNZ said.
Despite the price increase, many consumers responded to the post saying that they understood the need to increase prices.
One fan of the business said: "We completely understand that prices have to go up. Thanks for not hiding it in smaller packages or changing recipes. We are grateful for good quality New Zealand made."
Others also said they were happy to pay a little more as long as the recipes stayed the same.
Whittaker's is one of New Zealand's most beloved brands.
The company has come on top of the Reader's Digest Most Trusted Brands survey for 10 years in a row.