Pulse Energy is the fifth and most recent company to start retailing electricity in Central Otago, where TrustPower has the majority of customers.
During the past month, Pulse has actively marketed its business - contacting residents about whether they wanted to switch from other firms.
Pulse sales and marketing manager Ashley Church, of Auckland, said "several hundred" had been switched - some from TrustPower - and to his knowledge all had confirmed their desire to do so.
But TrustPower community relations manager Graeme Purches said when some clients had been contacted by the company after it received "switch files" for them from Pulse, they were surprised and indicated they did not want to change.
In general when TrustPower received switch files from other retailers for its customers, it immediately contacted those clients to confirm their decision to switch and enable the process, he said.
Mr Purches said last week in the past two weeks about 70 switch files had been received from Pulse for Central Otago TrustPower customers, and "about half" of those denied wanting to switch when contacted by TrustPower.
"They told us they requested more information from Pulse, but did not ask to be switched.
There is a real risk that people are going to get confused about this."
Mr Church disputed up to 35 customers had been switched without consent, but said if any potential customers had been switched inadvertently, Pulse would immediately rectify the situation.
"While we have robust systems in place, we certainly take those concerns seriously and will check our systems to ensure that no client is being inadvertently switched where it is not their intention to do so.
We encourage anybody in that position to contact us because we would like to deal with it immediately," he said.
Mr Church said Pulse had also received calls from TrustPower customers who wanted to switch to Pulse, but when faced with a breach of contract fee of up to $95 they changed their minds.
He said of customers who had switched from all existing retail companies, only some of those from TrustPower had cited problems.
Mr Purches said to his knowledge the cost of switching or breaching a contract - applicable in some circumstances - was not an issue.
