The sudden sackings may also expose the government to legal action, though if any of the trio did mount a challenge it would be almost impossible to win damages.

The federal bureaucracy was stunned on Wednesday when, on his first day as Prime Minister, Mr Abbott announced the departure of three serving departmental secretaries: agriculture's Andrew Metcalfe, industry's Don Russell and resources' Blair Comley.

Mr Abbott gave no reason publicly for their removal, saying simply that each had ''made a substantial contribution to public life in Australia and I wish them well for the future''.

However, public service sources speculated that they were dismissed in retaliation for perceived political slights.

Mr Abbott has no actual power to terminate a secretary's tenure; only Governor-General Quentin Bryce is authorised to sack a department head.

To do this, she would have needed a recommendation from the Prime Minister. However, Mr Abbott had been in the role for barely an hour before announcing the departures of the three secretaries.

And, under the Public Service Act, he would have required reports on the proposed terminations from Public Service Commissioner Stephen Sedgwick and from his own department head, Ian Watt, before approaching Ms Bryce.

Ms Bryce's office referred media inquiries to the Department of the Prime Minister and Cabinet. The department said on Thursday ''that the provisions of the Public Service Act were complied with'' but would not say when the reports were written.

The Federal Court has previously ruled that departmental secretaries must be given procedural fairness - including the opportunity to put their case - before any recommendation is made to dismiss them.

This followed a challenge by former Defence Department head Paul Barratt, whom the Howard government sacked controversially in 1999 after he had been in the job for about a year.

The three departing secretaries will now be entitled to payouts amounting to a year's pay.

The reported total salary packages of the trio, as of July, were $665,600 for Dr Russell, $649,220 for Mr Metcalfe and $632,840 for Mr Comley.

Dr Russell was widely regarded as a marked man once the Coalition won office as he was very close to former Labor prime minister Paul Keating.

Mr Comley, a past head of the now abolished Climate Change Department, was a key architect of the former government's carbon price.

The loss of Mr Metcalfe - the most experienced public servant of the three - was more surprising, given he had previously worked in a Liberal minister's office.

However, he was seen by some as an unnecessarily public proponent of Labor's Malaysian refugee solution and a critic of the Coalition's ''turn back the boats'' policy.

Mr Metcalfe told his staff on Wednesday: ''Today is my last day as a member of the Australian Public Service.

''While I am naturally disappointed that I will no longer be working with you, I of course accept and respect the government's decision.'