Some 67 military properties are slated to be sold off by the federal government to raise funds, including Sydney's Victoria Barracks - a complex established in 1840.
Between 450 and 650 personnel and their families based at the barracks will be relocated to other defence sites.
NSW Liberal MP James Griffin said he had grown up on Victoria Barracks, in the Sydney suburb of Paddington, because his mother was its first female commander.
"I've seen what's inside there," he told reporters on Wednesday.
"The community it holds, the place it holds in the heart of defence members that live on base and have served there over many many years."
A defence department spokesperson said it was going ahead with the planned sale, with personnel to be moved off the site by the end of the year.
"The transition and divestment of Victoria Barracks Sydney will be managed carefully and sensitively, supporting our people, families and the broader defence community while preserving its heritage, history and legacy," they said.
Extensive planning had been done to minimise disruption, they said.
A rally will take place outside the barracks on Sunday, with thousands expected to turn out.
Voices across the political spectrum have railed against the move, with none more high profile than former prime minister John Howard.
On Wednesday, he announced plans to attend and speak at the rally.
"Like many in the community, I resent the Albanese government's indifference to our proud national and military history in proposing the sale of sites which are part of that history," he said.
Federal independent Wentworth MP Allegra Spender and state independent Sydney MP Alex Greenwich also backed the call.
NSW RSL president Vince Williams said the site was an important strategic location.
"We must retain ownership of it because in five or 10 years time, when people realise it is a strategic asset and it needs to be occupied, it will be too late," he said.
Premier Chris Minns has jumped into the fray to challenge his federal Labor colleagues.
He supported the idea of listing the military site on the state's Heritage Council register.
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