Telco giant Telstra is suing the National Broadband Network Company (NBN Co) over a commercial dispute that could be worth more than $100 million.
Telstra began legal proceedings in the NSW Supreme Court late on Tuesday over consumer price index (CPI) adjustments.
Under an $11 billion deal finalised in June 2011, Telstra was to receive $9 billion so NBN Co could access its underground pits to install fibre optic cables, with payments adjusted for inflation over a 30-year lease.
But the parties are in dispute about CPI adjustments, with Telstra wanting indexation to begin on January 1, 2012 - a year earlier than NBN Co's preferred date.
"We have one take on the contract and NBN Co has another," a Telstra spokeswoman told AAP on Wednesday.
"We have not been able to reach agreement through a long mediation process so, as provided for in the contract and as the next step, Telstra is asking the court to decide.
"The impact to us over the term of the agreement is significant, but not material from a market perspective."
The structural separation undertaking of Telstra's retail and wholesale arms came into force in March 2012, following approval from the Australian Competition and Consumer Commission.
