The creation of a new federal government ''super-department'' in 2014 would fly in the face of advice from the nation's most senior bureaucrat.
The Abbott government proposed the idea on Tuesday of merging the Department of Human Services with the recently expanded and renamed Department of Social Services.
But the move would be against the advice of Prime Minister and Cabinet departmental secretary Ian Watt, who warned last month of the danger of ''endless tinkering with the bureaucracy''. The idea was also slammed by the main public sector union on Tuesday, with the CPSU describing it as an excuse for more public service job cuts.
The merger would bring DHS and DSS, formerly known as FaHCSIA, together to create a department of more than 40,000 public servants. It is being considered by the government's Commission of Audit, which is due to front a Senate committee in Canberra on Wednesday.
But in his keynote end-of-year speech in Canberra in December, Dr Watt said that machinery of government changes should be made quickly and at the start of a new term of government.
''MoG changes can be expensive and disruptive - we know that and governments know it too,'' Dr Watt said.
''Governments also appreciate that if you want to get the best out of departments and agencies, you shouldn't endlessly tinker with bureaucratic structures.
''Rather, when you want to make a significant change, you do it, and you do it at the start of a new term.
''In future MoG changes will be concentrated after elections and will be minimal between elections.
''It's just too difficult for substantial MoG changes in the term.''
There were substantial machinery of government changes in the first months of the Coalition government with nine departments renamed, three abolished, two created and about 10,000 public servants moved about.
Dr Watt was still on leave on Monday and unavailable for an interview.
Social Services Minister Kevin Andrews, who announced the merger idea on Tuesday, said a new super-department could save money on backroom operations.
''There are certain things that could be brought together,'' Mr Andrews said.
''There would be savings in terms of computer and IT systems and back-of-office functions, so any prudent government will consider the options.
''This is not about redundancies, this is about how we have the most efficient and effective form of government.
''This is the major interface of the Australian public with the Commonwealth Government in terms of Medicare, in terms of Centrelink, and a whole range of services.
''We want them to be effective and efficient.''
CPSU deputy national secretary Louise Persse said she suspected the idea was about cutting jobs.
''Frankly, this just looks like another Coalition job-cutting exercise,'' Ms Persse said.
''Have you recently tried to access a social service, and might a merger lead to improvements or problems?
''This area is already really feeling the strain of the job cuts that have gone on over the last couple of years, and our members are really concerned about the prospect of further cuts.''
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