But Mathias Cormann will not say why public service departments want to strip away the legal protections from the generous superannuation benefits enjoyed by Commonwealth bureaucrats.

The Minister railed on Friday about "baseless scaremongering" by unions after reports that public servants' employer-funded super contributions could be cut by up to 30 per cent.

The Canberra Times revealed that several major departments are moving to scrap their workers' legally binding entitlement to the Australian Public Service's generous 15.4 per cent employer superannuation contribution.

The Community and Public Sector Union says the move would enable the government to strip hundreds of thousands of dollars from the retirement dreams of its bureaucrats at the stroke of the Finance Minister's pen.

But Senator Cormann said the government had no plans to change the guaranteed super rate for public servants.

"This is baseless scaremongering by the CPSU without foundation," the Minister said.

"There is absolutely no plan to reduce super contributions for those federal public servants in super accumulation schemes.”

The Commonwealth workplace authority, the Australian Public Service Commission, which is enforcing the Abbott government’s tough industrial line in the service, refused to answer questions about the contentious plan by departments.

But the Department of Human Services, the Australian Taxation Office, the Department of Health and the Finance Department, which together employ nearly one-third of the Commonwealth bureaucracy, have already made their wishes regarding their workers’ super guarantees clear.

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

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

The CPSU, the main public sector union, says the move would leave the nest eggs of Commonwealth bureaucrats vulnerable to cost-cutting by a finance minister who would have the power to unilaterally cut employer contributions.