The ACT Greens are opposing the sale of the East and West blocks in the parliamentary triangle amid concerns of the impact of privatisation on national heritage.
The blocks are set to be sold off as part of a federal government plan to divest assets. The National Archives, housed in the East Block, will temporarily relocate to Old Parliament House as capital works are undertaken. The archives were expected to return to the block in late-2018.
The sale of the East and West Blocks will result in the first private land ownership in the parliamentary triangle, which encompasses Parliament House, Old Parliament House, the High Court and the National Gallery. The sale has been criticised by heritage experts and the federal opposition.
ACT Greens leader and tourism spokesman Shane Rattenbury will put a motion to the Legislative Assembly this week calling for action on the issue.
"If the East Block and West Block offices are privatised, the federal government will lose control of the heart of Canberra's national area and the National Capital Authority will come under pressure to approve unsuitable commercial development," the motion reads.
Mr Rattenbury said more life could be brought into the precinct without privatisation.
"For example, long-term leases to hotels or other tourism entities would mean government both maintains and protects our precinct's heritage, both for the city and nationally."
Greens heritage spokeswoman Caroline Le Couteur said the decision to sell the blocks was "deeply concerning", and a blow to national heritage.
"The parliamentary precinct has huge national heritage importance and should not be privatised," Ms Le Couteur said.
Amendments to the National Capital Plan to allow for the privatisation of the buildings were made in 2016.
Minister for Finance Mathias Cormann said there were no public submissions received through the consultation process on those changes.
"Private investment provides an opportunity to revitalise these properties and ensure their significant heritage values are maintained," Mr Cormann said.
"Heritage values will be protected through covenants and provisions included in the sales contracts and Crown leases."
The blocks are now zoned for mixed use, which would allow for private sector offices, hotel accommodation or serviced apartments.
"These buildings will not be able to be used for residential purposes," Mr Cormann said.
ACT Chief Minister Andrew Barr said he supported the sale.
"The government's view is that the heritage values of these buildings should be respected and they are well suited to some kind of adaptive reuse, as hotels for example," a spokesman for the chief minister said.
He added that the ACT government had no interest in acquiring the buildings.
The East and West Blocks were designed by Old Parliament House architect John Smith Murdoch.
Built in 1925-26, East Block has been home to the Archives since 1998 but was once the General Canberra Post Office and the point from which all distances in Canberra were measured.
West Block was opened for government use in 1927 and was once home to the National Library, the Crown Solicitor's office and the Australian Electoral Commission. It is currently vacant.