Spark will lift prices for some broadband and landline plans from February as a result of the Commerce Commission's decision to increase wholesale copper line charges.
Home landline customers in Auckland, Wellington and Christchurch will pay $3.50 per month more, while ADSL/VDSL broadband customers are facing a $5 monthly increase.
On Tuesday, the commission announced that the wholesale price for access to Chorus' copper network would be raised to $41.69 per month.
The regulator came to the final figure, $3 higher than expected, after it conducted a more rigorous process to find the price than the initial pricing principle review, which relied on international benchmarks.
Spark said the new Chorus charges, which took effect yesterday, were almost $8 per month higher for broadband services and $7 higher for landline voice services.
Spark's Jason Paris said he was disappointed about the price increase.
"We have worked hard over the past few years to keep prices as low as possible, and we want to keep them that way," Paris said.
"However, this regulatory decision means a significant and unexpected increase in our underlying costs, so unfortunately we have been forced to reflect these costs in our customer pricing."
He said the decision not to backdate when the new Chorus line charges came into effect was the only good news in the regulator's pricing decision.
"In light of the Commerce Commission's earlier threat of backdating, we put up our prices in February this year," Paris said.
"At the time, we said that if there was no backdating, we would do the right thing and return savings where we could to customers who were affected by the price increases in February and remained on their impacted plan."
Paris said eligible home landline customers in Auckland, Wellington and Christchurch would receive a credit on their monthly bills, while eligible 40GB and 80GB ADSL/VDSL broadband customers nationwide would have the choice of a few options, one of which would be an account credit.
Spark said it would proceed with the credits from March, provided there were no appeal proceedings.
Home landline customers outside the three main centres will not receive any credit, but their prices will not be increased in February, the company said.
Spark added that ADSL/VDSL customers on Unlimited plans would also not be eligible for a savings credit, as their plan prices did not increase earlier in the year and were instead reduced by $10 a month.
Ultra Fibre broadband plans will not face price increases, as their services are not dependent on the copper network.
The regulator's decision sent Chorus' share price soaring.
It will boost the firm's annualised operating earnings by $120 million.