Telecom says one of its mobile phone rivals is taking advantage of the rules on text messaging, and costing it tens of thousands of dollars.
2degrees is running a contest in which customers can win prizes by receiving a certain number of texts in a given time period.
Under the current mobile termination rate system, Telecom has to pay 9.5 cents to 2degrees every time one of its own customers texts a 2degrees phone - and vice versa.
Telecom says the 2degrees Text Me Race encourages spamming and is starting to put a serious load onto its system.
But 2degrees says the contest highlights the flaws with the system - which it says is designed to stifle competition.
The Commerce Commission last year proposed doing away with the termination rates for texting altogether saying they were uncompetitive.
The Commission will release its final decision on that on 28 April.