Labour says New Zealand soldiers' deaths in overseas battlefields will no longer have independent scrutiny if changes to the Coroners Act go ahead.
Defence spokesman Phil Goff said amendments to the legislation will block a coroner from launching an inquiry when a New Zealand Defence Force member is killed in hostile action overseas.
The coroner will be able to report on a soldiers' death only if given approval by the Attorney-General, and the coroner cannot make any recommendations after an investigation.
Mr Goff said in a statement: "Having military deaths only investigated in-house raises suspicions that this is a convenient way of closing down investigation and criticism of Government and Defence Force decisions and mistakes."
Mr Goff released advice from officials, who have expressed concerns about the amendment.
Officials said the changes would mean there was no mandatory requirement for an investigation into soldiers' deaths overseas.
They also said the amendment appeared to be a response to a single case -- a coronial inquest into the deaths of soldiers Luke Tamatea, Jacinda Baker and Richard Harris in Afghanistan 2012.
Official documents said the coroner's inquiry in that case "made comments that appeared to be commentary on matters that were non-justiciable, in particular examining operational decisions of commanders".
Mr Goff said families of Defence Force personnel killed overseas have pointed out the value of having an independent, civilian officer examine evidence and make recommendations.
The law change comes as New Zealand sends 143 soldiers to Iraq to battle the Islamic State (ISIS).
Mr Goff said: "With Kiwi troops commencing another deployment to a high-risk environment, first and foremost it's important that decision-makers do everything possible to keep them safe.
"Should a tragedy occur however, families of soldiers and the New Zealand public need to know that proper and independent scrutiny will take place, and that lessons are learned to prevent any mistakes being repeated in the future."
By Isaac Davison of the New Zeland Herald
