The government has had to bring an urgent bill to parliament to validate some of the speed limits set by local councils since 2004.
Transport Minister Simon Bridges says the legislation, which will be passed through all its stages on Tuesday, will ensure that speeding tickets "issued in good faith" will be legally valid.
He says it's not known how many drivers or infringement notices may be involved, but that's a moot point because they will all be valid.
Local Government Minister Paula Bennett says the problem came to light when it was realised some councils hadn't renewed their speed limit by-laws.
She says there was confusion about the legislative framework after changes were made to local government legislation in July 2002 and June 2006, as well as changes to transport legislation in April 2004.
Mr Bridges, who is taking the bill through parliament under urgency, says his priority is to ensure public safety through the maintenance and enforcement of speed limits.
"For that reason, the government has moved swiftly to eliminate confusion, protect the public and fix the potential problem," he said.
The first reading of the bill is being debated, and the government is facing criticism from opposition parties for taking so long to find out there was a problem.