"This item had the potential to cause interference with other licensed services creating issues with people's safety," MBIE compliance officer Fadia Mudafar said.
"Breaks in the signal would result in poor communications with a risk for misunderstanding. Any interference is a significant safety risk."
Fishpond.co.nz claims to have millions of products available for sale, including books, toys, electronics kitchen and beauty products, which are largely sourced from overseas.
According to MBIE, Fishpond.co.nz had received five warnings since 2011 for advertising radio communications equipment for sale that did not comply with New Zealand law.
The company had also been charged on two occasions since 2013 by other Government entities for breaches of New Zealand's regulatory framework.
The company was fined in the Manukau District Court under the Radiocommunications Act and the Radiocommunications Regulations Act.