The loss of an important court file related to the Pike River disaster is being treated as a matter of serious concern.
Lawyers representing two victims' families asked to see a file that explained a controversial district court decision to drop health and safety charges against the mine's former chief executive Peter Whittall, following an offer of compensation.
It took more than a year before they were advised parts of the file were missing.
The West Coast-Tasman MP, Damien O'Connor, said the court's response that a search was continuing wasn't good enough.
He said it was odd that one government department could lose important files that might implicate another government department through a court process.
The Council of Trade Unions have said that the loss is disgraceful.
The CTU's president, Helen Kelly, said an investigation into court systems was needed to ensure this does not happen again.
"The Minister of Justice should be very, very concerned that what is a massive massive potential manslaughter criminal investigation in New Zealand is treated with such disregard by our court."