A drink-drive lawyer estimates around 85,000 motorists could have their drink-driving cases reviewed over a word in a police advice script.
Lawyer Alastair Haskett has told Stuff that after successfully winning a string of cases relating to the official wording, there could be six year's worth of similar convictions that could potentially have their cases revisited.
That could amount to 85,000 motorists.
Haskett said it came down to the police using the word "prosecution" when the legislation used "conviction".
Motorists who blow more than 400 micrograms of alcohol per litre of breath are held by the police.
The officer then reads a prepared script giving the detained driver an opportunity to phone a lawyer and have a blood test.
Stuff reported that, until recently, the script advised the motorist their breath test result could be used as "conclusive evidence in a prosecution against you".
But the legislation stopped police from using the breath test as evidence unless the motorist was warned their result could be used as "conclusive evidence to lead to your conviction".
An Auckland District Court judge recently dismissed a charge of drink-driving against one of Haskett's clients, agreeing with the lawyer that there was a "material difference" in the meaning of the words "prosecution" and "conviction".
"The police have decided not to use the word Parliament requires, have directed officers to use the wording set out in Block J, have persisted with that despite at least two decisions of the district court dismissing charges for non-compliance with [the legislation] and the police have not appealed those two decisions," said Judge Russell Collins.
An internal police memorandum revealed senior police officers were aware of a potential problem when they were drafting the script, known as Block J, in 2014.
Documents released under the Official Information Act by police revealed the query was "considered – not amended".
Police refused to comment, saying the drink-drive case had been referred to Crown Law to consider appealing.
Meanwhile, Stuff report the police are understood to have recently changed the wording in Block J to include the word "conviction".