The Ministry of Justice mistakenly sent thousands of people a text message telling them they had an unpaid fine.
The message, which asked people to call the ministry's unpaid fines number, was sent to about 29,600 people this morning, ministry legal and operational services deputy secretary Nigel Fyfe says.
"Through human error some people who have already paid their fines incorrectly received the text message."
The ministry had sent a follow-up text apologising and telling people to disregard the earlier text if they had already paid their fine, he said.
"We looked at how this mistake was able to happen and have made changes to prevent it happening again," Mr Fyfe said.
The extra traffic on the phone line in the morning caused 20 minute delays for callers.
"We again apologise to people who received the message in error, but urge those with outstanding fines to make contact with us in the coming days."