He said the loss of a strong and established base risked a slower response time in civil defence emergencies, such as when Hauraki soldiers "hit the ground running" within two hours of an emergency being declared for Tauranga's devastating 2005 storm.
The Hauraki Battalion also supplied headquarters and logistical support for the Rena disaster.
Hauraki Association president Des Anderson put it bluntly: "We don't like the idea."
Experience had shown where the army closed its halls and reduced its presence, territorial soldiers no longer related to the new environment and recruitment dropped, Mr Anderson said.
"Slowly the Haurakis will start losing out."
A former commanding officer of the battalion, Lieutenant Colonel Warren Banks, said the Hauraki battalion was unique among New Zealand's territorial units for having never amalgamated, tracing its history directly back to its formation in 1898.
It was one of the few army units in the world to have never amalgamated.
He said the Haurakis was all about family, both in the regimental sense and in the way that generations of Bay families had served as territorials.
"It is ours and it is what we are proud of.
"The uniqueness of the battalion is what we treasure the most."
Colonel Banks estimated the number of full-time regular force soldiers with the battalion could drop by a third to about three personnel while the three or four civilian staff at the Army Hall could lose their jobs.
He was optimistic that the Minister of Defence Jonathan Coleman would not close the hall because of its importance to the Haurakis and as a venue for many other uniformed organisations.
A letter to Dr Coleman from six former commanding officers and senior NCOs said the future of the Territorial Force was being placed in jeopardy by the army reorganisation - including halving the number of territorial force units to three.
The letter said the Haurakis were not only a good recruitment avenue to the regular force but sponsored a number of cadet units that were an integral part of the community.
"The future of these units is also being jeopardised," the letter said.
Dr Coleman replied that retaining the Haurakis as a separate unit would be unlikely under the proposed reorganisation which was intended to more efficiently align territorial units with their regular force counterparts.
"I understand your concern that a reduction in numbers would restrict the ability of the Territorial Force to produce high-calibre officers, NCOs and soldiers. Please be assured that there is no proposed reduction in Territorial Force numbers."
Mr Coleman said "regional representative responsibilities" would help ensure the history of the Hauraki Battalion was maintained.