The Commerce Commission has confirmed it has launched a preliminary investigation into the marketing and sale of water filters by the company HRV.
The watchdog has confirmed to RNZ it has complaints from Whanganui, Amberley and Nelson.
The investigation began this month and the Commerce Commission is in the early stages of assessing the complaints to determine whether to go further with its inquiries.
HRV chief executive Bruce Gordon describes the investigation as very low level and said he didn't have any concerns about it.
"There's no need to address any of the process. We perform as a direct marketing company, alongside hundreds of other companies in the market. We are probably the most well-positioned of the companies, in terms of processes and systems and compliance with the likes of the Fair Trading Act and Door to Door Sales Act."
Earlier this month, HRV rejected claims from Age Concern that its salespeople had been pressuring Havelock North residents into buying water filters during the town's water contamination emergency.
HRV denies any fault, and has previously said all of its salespeople were pulled from the area.