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."
He is among a group of state and federal MPs across the political spectrum calling for Prime Minister Anthony Albanese to intervene in the sale.
A rally will take place outside the barracks on Sunday, with NSW Labor MP Marjorie O'Neill saying police expect numbers into the thousands to turn out.
"It's going to be an absolutely pivotal day to get that message to the prime minister: now is a time to intervene," Dr O'Neill said.
"Victoria Barracks are far too important to be sold off. It is the spiritual home of the army."
The site should be opened up more to the public, the Coogee MP said, and be used more for events like sporting matches.
"Senior ADF officers, time and time again, have requested and wanted this site open, but have been met by the bureaucrats ... and stopped," Dr O'Neill said.
Federal independent Wentworth MP Allegra Spender, and state independent Sydney MP Alex Greenwich also backed the call.
"I have raised this directly personally with the prime minister, and I think it is going to take public pressure to move this government on this because they seem pretty adamant right now," Ms Spender said.
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.
NSW 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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