Alinta Energy has been fined $300,000 over the transfer of more than a dozen Victorian customers to the company without their consent.
The transfers were arranged between September and October 2016 by three sales agents acting on behalf of Alinta, without the customers' explicit informed consent, the Essential Services Commission said.
Alinta forked out $300,000 for 15 penalty notices after some of the customers - from areas including St Kilda, Morwell, Croydon and Warrnambool - complained to the commission.
In a statement, Alinta said its investigation found three "supplier" agents were attempting to defraud the company and customers by signing them up without consent.
It reported the fraud to the commission and ensured the sales workers were deregistered.
"In many cases the behaviour was detected and reversed before the customers' accounts became active or a bill was issued," the company said.