Sending marketing emails to people who did not want them has cost the Warehouse $19,800 in fines.
The shopping chain was warned four years ago about the practice but complaints came in again this year.
Department of Internal Affairs electronic messaging compliance manager Toni Demetriou explains what went wrong.
"It's really important with our legislation and the approach that we take that 'unsubscribe' from electronic messages, commercial electronic messages, is honoured within five days from that request being made.
"And, in this case, things weren't working in their environment, which meant that people that were trying to unsubscribe kept receiving marketing messages."
Mr Demetriou said he hoped the Warehouse did not repeat the mistake.