Labour MP Grant Robertson said he had been told the current "ingestor" or software used to make the digital records available online would take four years to complete the task.
Faster software was to be developed under the troubled Government Digital Archive Programme which was canned last month.
"This is potentially going to mar the WW100 commemorations", he said.
"I understand that this has been described as the cornerstone of a number of WW100 projects."
"I think the families of WW100 veterans have been let down here by the Government and this is just another example of the IT failures that have bedevilled this Government but also I think it's a failure of leadership within the Department of Internal Affairs to recognise there were problems here and solve them earlier."
Acting Chief Archivist and General Manager Archives NZ John Roberts said more than 85 per cent of the records had been digitised and 46 per cent were currently viewable online free of charge.
While Archives NZ was committed to publishing online all of the personnel records via 'click to view' to meet the anniversary deadline; "until this process is complete the records will still be available on request" Mr Roberts said.
However that records by request service usually had a 48 hour turn-around and carried a $25 charge.
Mr Roberts said Archives NZ was still confident of meeting the August deadline, "at this stage".
NZ's First World War Service Records online:
* When finished will comprise of 160,742 files, which range in size from three pages to over 600
* In total this amounts to some four million digital images.
* The first file published online, on December 1, 2009, was that of Henry William Bourne Palin, the great uncle of English comedian, actor, writer, and television presenter Michael Palin.
* That file and 73,373 others may be viewed by searching for a person's name in the Archives NZ online catalogue Archway at: archway.archives.govt.nz
