Unions say the move would enable the Commonwealth to strip hundreds of thousands of dollars from the retirement dreams of every bureaucrat, at the stroke of a minister’s pen.

Several departments are moving to scrap their workforce’s legally binding entitlement to the Australian Public Service’s generous 15.4 per cent employer superannuation contribution.

If successful, the move would leave Finance Minister Mathias Cormann free to slash the rate of employer contributions to public servants’ super by more than 30 per cent to the 9.5 per cent guaranteed to all Australian workers.

The Australian Public Service Commission, the Commonwealth workplace authority that is enforcing the government’s tough industrial line in the public service, refused to answer questions on Thursday about the departments' contentious plan.

The Department of Human Services, the Australian Taxation Office, the Department of Health and the Department of Finance, together employing nearly a third of the Commonwealth bureaucracy, have already put their cards on the table on their worker’s super guarantees.

The departments want to take their public servants’ superannuation guarantees out of their legally protected enterprise agreement and put them into “regulations”.

Departmental secretaries say they have no plans to cut the rate of contributions and that they are moving to “streamline” and “simplify” cumbersome enterprise bargaining agreements, many of which run to more than 100 pages.

However, the principal public sector union, the Community and Public Sector Union (CPSU), says the move would make bureaucrats' superannuation hopelessly vulnerable to cost-cutting drives by a finance minister who would have the power to unilaterally slash employers' contributions.

The public service’s generous superannuation provision is a draw card for workers joining, and staying at, government departments, and the Commonwealth’s various retirement savings schemes are a hot-button issue in the bureaucracy.

Superannuation is the latest battleground to emerge as 117 agencies and departments try to trash out new workplace deals with 160,000 public servants.

Already fights are raging about wages, working hours, allowances and other issues as departments slowly disclose their offers.

CPSU national secretary Nadine Flood said modestly paid rank-and-file government employees were worried about their retirement savings. “As bargaining continues, the number of significant Commonwealth agencies trying to remove the superannuation contribution from agreements is growing,” she said.

“The Department of Human Services (DHS) is the most advanced in its plan to strip superannuation from agreements, but we’ve got Health, Tax, Finance and the Australian Institute of Criminology following in its wake.

“So this is starting to look like a whole-of-government direction, but we’re not at the point yet where we can say it absolutely is.”

Ms Flood cited the government’s biggest department, and her union’s stronghold, Human Services, and its largest group of workers at the APS4 classification who earn less than $69,000 a year.

She said Centrelink, Medicare and Child Support Agency workers would lose more than $4000 annually if their employer's super contributions were cut to 9.5 per cent.

“This is causing enormous concern in DHS, with staff worried their super cut be cut to 9.5 per cent,” Ms Flood said. “The Public Service Commission needs to answer the question; why are multiple agencies in different portfolios all saying they have to strip the superannuation out of enterprise agreements?”

On Thursday, the Public Service Commission said it would not answer questions. “The APSC does not comment on the advice we provide to agencies,” a spokeswoman said.