Consumer New Zealand says power companies are failing to properly manage requests to switch suppliers.
Some people complain they have been switched without their consent, while others say their supplier has refused to make the change.
Consumer NZ chief executive Sue Chetwin says she logged on to a switching site to test it. Despite later telling the power company she had changed her mind, they switched her anyway, even though the household account is not in her name.
Ms Chetwin says her case highlights the problems faced by some consumers.
Bruce Simpson of Tokoroa says he tried to switch from Genesis to Pulse last year but three months later was still getting bills from Genesis. Both companies said the fault lay with the other firm, he says, so he had to re-apply.
Not widespread - TrustPower
New Zealand's fourth largest energy retailer, TrustPower, says the problems are not widespread.
Community relations manager Graeme Purches says small player Pulse Energy isn't following protocols, and is accounting for many of the mistakes.
Of the country's 1.95 million electricity consumers, about 26,000 (1.3%) changed supplier last month.
Energy Minister Gerry Brownlee says that he will be writing to power companies urging them to lift their game, and that he is prepared to regulate if necessary.