Parliament has passed legislation under urgency to validate an administrative error by police over the swearing in of 63 returning police officers.
It is the second time that Parliament has had to fix the law because police have failed to correctly carry out oaths under the Police Act.
Police Minister Anne Tolley says the 63 officers returning to the force were sworn in by District Commanders or Inspectors between October 2009 and July 2013.
She told Parliament on Thursday that under the Act, the oath can only be administered by the Commissioner or someone authorised by the Commissioner.
"The bill will deem the oaths taken by affected constables to have been administered as if the persons administering the oaths have been approved by the Commissioner of Police. It will remove any doubt about the validity of the actions of the affected police employees."
In 2009, the law was changed under urgency relating to the oaths of new recruits.
The Labour Party's police spokesperson, Jacinda Ardern, said the Police Minister should have checked that oaths were being done properly throughout the police.
"We all know about the concept and importance of constabulary independence, but that certainly shouldn't mean distancing yourselves so far from you role as Minister of Police that's not even your constables are being sworn in properly."
The leader of the House, Gerry Brownlee, told Parliament the legislation was embarrassing for police.
The Green Party says the Auditor-General needs to investigate how police could have made the error.
The Police Commissioner will carry out an internal investigation to find out how police came to make the error.