Telecom is considering its next step after losing in the Court of Appeal over competitive pricing in the data tails case.
In 2009 Telecom was hit with a record $12 million fine from the High Court in Auckland for charging its competitors disproportionately high prices to use its network between 2001 and 2004.
Telecom appealed against that decision.
In Monday's Court of Appeal judgement, Justice Glazebrook dismissed Telecom's appeal saying that Telecom's breach was significant.
The court has not released its decision on the penalty.
The Commerce Commission says the ruling is important as it reinforces the fact that it is illegal for a business to use its market power to deter or prevent rival businesses from competing effectively,