The Returned and Services Association says it is preparing a strategy to fight to keep the current New Zealand flag, and has criticised the timing of a new committee to debate its future.
Last month, a 12-person committee was announced to look into whether a change was needed, before public consultation and a postal referendum.
But the RSA said it was unacceptable that the new committee would come just before the ANZAC centenary, and that the $26 million cost of the review project was excessive.
National president BJ Clark said they were working on a plan to fight to keep the current flag, and would unveil it after ANZAC day.
He said New Zealand forces had served and sacrificed under the flag, which was as relevant today as it was when troops landed in Gallipoli.
"I'm not sure why we should got through a process of picking a number of flags first then putting it up against the existing flag, only to find there's an overwhelming majority of people who don't want change."