The public sector union has seized on comments from outgoing Treasury Secretary Martin Parkinson, that his department could no longer "work harder and longer" to make up for cuts.
Dr Parkinson, who leaves in July, a victim of the government's purge of senior bureaucrats, told the Institute of Public Administration his department would shrink from a peak of 1100 workers in 2011 to as few as 730 in 2017 - meaning one in three jobs would go.
''In the past, our response to increased demands was to increase our efforts: by working harder and longer. Needless to say, this is not sustainable,'' he said in the speech.
Community and Public Sector Union national secretary Nadine Flood said 5000 jobs had gone from the public service since September, and the Government - and public - could not not expect the same level of services.
“Our members have been saying for years that the public service is not a magic pudding, that successive cuts are taking their toll on their ability to deliver the policy and services that this country deserves,” she said.
“If this government is seriously considering cutting anywhere between 14,500 and 26,500 jobs then it needs to lower people’s expectations of government.”
She said in a statement that the Government ought listen to the "experienced voice" of Dr Parkinson.
“His warning should prompt a sober and wide-ranging debate over what we as a society expects of government,” she said.
“The community expects high-quality services and it is up to the government to ensure they are fully funded and properly resourced.”
Dr Parkinson also used the speech, one of his last before leaving office, to highlight his success in reversing a century of male domination within the department.
"Treasury has long had a low proportion of women in our leadership group," he said.
"We wanted to get to the bottom of this imbalance, trying to understand the barriers to the recruitment, retention and progression of women."
In more bad news for Canberra's local economy, Dr Parkinson said he wanted more Treasury staff working from Sydney, home of much of Australia's capital market activity.