Canterbury lines company Orion says a Commerce Commission decision to almost halve its planned price rise means it will have to increase its debt to carry out necessary work.
Orion wanted to increase its charges by an average of $8.50 a month, but this has been restricted by the commission to an average of $4.80.
The increase would be added to bills from April 2014 for four years.
Orion chief executive Rob Jamieson says the full increase is needed to do work that will make its network more resilient and to repair earthquake damage.
Under the Commerce Act, the company needs permission from the Commerce Commission to do this.
Orion says its shareholders - the Christchurch City and Selwyn District councils - will take a hit, as the company has to increase debt to carry out the work.
Commerce Commission deputy chair Sue Begg says some of Orion's proposed increases also covered lost revenue following the earthquakes.
Ms Begg says these costs need to be shared between Orion and the customer, rather than put on the customer alone.
Rob Jamieson says Orion will closely look at the decision and decide if they will appeal.