Broadband customers have complained that they have been tricked into moving internet providers without their consent.
In one case, a sales rep called an internet provider pretending to be the grandson of a customer and saying they wanted to set up a fibre internet connection.
Whangarei resident Rosalene Bradbury told the Weekend Herald that in the past weeks salespeople had approached locals in the One Tree Point area, where mostly elderly retirees live on their own.
She said the salespeople claim there are pre-existing contracts for broadband fibre services between the householder and Vodafone. Bradbury is a customer of Northland internet provider Uber Group, and not Vodafone.
The customers are then asked for account details with their existing provider, and told they must either honour the contracts and move to Vodafone, or cancel them over the phone, a process that can involve waiting on hold for long periods.
"In my own case a man ... without identification, knocked on my unlighted front door at 6.45 on a very dark night," Bradbury said.
"I opened the door because I was not alone - would not have done so otherwise - to be told that my recently installed fibre needed to be checked. This person was asking for entrance to my house," she said.
Bradbury did not let the salesman into her house and ordered him off the property. She described the experience as "scary" and said others in the area had encountered similar visits after dark and voiced concern about them on Facebook.
A Vodafone spokeswoman said the telco was working in the area to encourage more of its customers to connect to fibre broadband if it was available at their addresses.
It had employed outside contractors for the sales push.
"In some cases, our representatives will go door-to-door to have these conversations," the spokesperson said.
"It is completely unacceptable for anyone to feel uncomfortable or threatened by door-to-door salespeople.
"We want to emphasise that this type of aggressive sales activity is prohibited under the terms of our agreements with third-party agencies operating on our behalf in the area.
"We have taken steps to retrain the teams operating in the area to ensure they are reminded of appropriate conduct," the spokesperson said.
Vodafone is asking that people who have been subject to the sales to contact the telco so it can investigate and take further action if necessary.
The practice of transferring customers from one telco to another without the person's consent is known as "slamming".
The Commerce Commission told the Weekend Herald it had received one complaint against Vodafone this year alleging slamming.
The commission has taken action over slamming in the past. In 2013 Slingshot was fined $250,000 over the practice. Its telemarketing firm Power Marketing was fined nearly $170,000 the following year over slamming.
Uber Group managing director Hayden Simon said his company had fielded many calls from customers complaining about sales tactics.
Simon said that in one phone call to Uber Group, a man used a false name and pretended to be the grandson of a customer to obtain the subscriber information necessary to move the customer over. An Uber Group representative rang the customer, who said he had not requested anyone - let alone his "grandson" - to move his broadband account.
The call recording was shared with the Weekend Herald, with the permission of the customer involved.
Simon said the sales push started early this month.
Uber Group alleged that at least five customers had been slammed to Vodafone in the One Tree Point area, but there could be more who had accepted the move without mentioning the reason to their internet provider, he added.
"Another customer again said that he was told that if he doesn't give his account number then he will lose his phone number when the service is installed by Vodafone, and there is a $2000 ... charge to pay," Simon said.
Simon believed many people who had allegedly been slammed would not have the time and patience to wait on hold for an hour or longer in order to cancel the transfers.
Northpower, the fibre broadband network infrastructure company in the Whangarei region, said it worked closely with the community to let them know when new ultra-fast broadband networks came to the area, but it was up to internet providers to connect customers and it would not comment on their business.
Geoff Thorn, chief executive of industry organisation the Telecommunications Forum, said telcos in New Zealand should not engage in predatory sales tactics like slamming customers.
Thorn said slamming was rare in New Zealand nowadays, especially for fibre broadband services.
He said there was no value for internet providers and telcos in annoying customers with such sales tactics, which wouldn't work in most cases. "There needs to be clear consent from the customer for the transfers to succeed," Thorn said.
He suggested that customers who believed they had been slammed should first contact their provider to file a complaint.
Jessica Wilson, head of research at Consumer NZ, said slamming was an outrageous sales practice.
"If you think you've been slammed, contact your telco. You should also make a complaint to the Commerce Commission if a sales rep has misled you. "