Spark plans to raise its prices for both phone landlines and broadband plans by up to $4.25 per month from 1 February.
It said the price hike was in reaction to the Commerce Commission's draft decision last week allowing Chorus to raise the price for using its copper lines.
Spark has previously said if that decision was confirmed, it would mean its annual costs would rise by about $60 million.
Spark's head of home, mobile and business Chris Quin said since the current price was set two years ago, competition has brought prices down.
"In the last two years the product that cost $75 today would have cost $105 two years ago. We've worked very hard to lower the costs for customers but this increase in our input costs can't be completely soaked up into our current prices," he said.
"We needed to make it clear what we were going to do with our pricing now for customers and we've committed that if the [final] decision is different next year...we will review this [our] decision again."