The fight to save the Sirius public housing building in Sydney's Rocks has been joined by the construction union, who have placed a Green Ban on the building which prohibits any unionised work force from working on the site.

The state government wants to demolish the 35-year-old building and sell the land to private developers with an approval scheme for 250 apartments. Residents and the union are angry the state government won't commit to redeveloping public housing on the site.

NSW Environment minister Mark Speakman rejected the unanimous recommendation of the NSW Heritage Council that the building be given heritage listing, saying that any heritage value of the building was "greatly outweighed" by the revenue a sale could bring. It is estimated the building could sell for $180 million.

"Unions will be standing side by side with residents to hold off demolition of the building," CFMEU NSW State Secretary Brian Parker told The Australian Financial Review. "The Sirius building is not only an important piece of Sydney's architectural history – it is one of the last areas of public housing remaining in the district."

The union has previously used a Green Ban effectively in the past; in the 1970s, the CFMEU's predecessor the Builders Labourers Federation was able to stop state government plans to demolish historic buildings in The Rocks which were home to many low-income residents. After the Green Ban was lifted, the public housing block that became the Sirius building was built. 

Sydney's newly reelected Lord Mayor Clover Moore is also against the sale of Sirius.

See also:

Government puts social housing ahead of Sirius preservation

Brutalist landmark awaits heritage decision 

Millers Point sales continue to run hot