Internal Affairs is looking into whether Telecom may have breached spam laws by sending text messages to customers that did not include instructions on how customers could unsubscribe from receiving such messages.
Telecom said its approach was "common practice", meaning Internal Affairs' ruling could have an impact on text and email marketing promotions run by other firms.
Victoria University law student Hamish McConnochie drew attention to the texts, promoting Telecom's pre-pay top-ups and roaming services, claiming they probably fell foul of the Unsolicited Electronic Messaging Act, passed by the last Labour government in 2007. The act states that all commercial electronic messages must include instructions on how recipients can unsubscribe, unless they have reached an "arrangement or understanding" with recipients that these need not be included.
Telecom sent customers text messages in November telling recipients that unless they objected then, Telecom would deem they had agreed future text messages from the company need no longer include an opt-out message.
Spokeswoman Anna Skerten said those messages created such an arrangement. But Mr McConnochie said simply not responding to that text did not meet the threshold for an agreement under the act.
Internal Affairs senior investigator Tony Demetriou confirmed the department's anti-spam unit was looking into a number of complaints about the texts.
It would not clarify in advance of its findings which interpretation of the law was correct.