Public Service Minister Eric Abetz has moved to clear up the confusion surrounding hiring practices that has dogged the bureaucracy since the new government took office in September, pledging to cut 12,000 public service jobs through natural attrition.

But the public sector union has reacted angrily, saying the move is a hiring freeze in disguise that will hit jobs and services in regional Australia and the bush.

Some departments have imposed recruitment freezes in the wake of the election, while others have ordered that any decision on new jobs must be approved at the very top.

But Senator Abetz announced that agencies must now demonstrate they have given existing staff every opportunity to apply for vacant jobs before hiring outsiders.

Agency and departmental heads are expected to hold staff briefings on Thursday afternoon on the new guidelines while the Public Service Commission works out the technical details of the ministerial order.

Senator Abetz said specialist and temporary jobs would also be able to be filled from outside the service.

"The new arrangements will maximise the use of capability already within the APS by increasing efforts to provide every employment opportunity possible to existing staff," he said.

"External advertising of APS vacancies and non-ongoing temporary employment will be limited to critical vacancies only, most particularly in specialist roles, where a suitable employee cannot be found within the APS."

Indigenous and graduate recruitment programs will also continue, he said.

"The government will ensure that these arrangements will not compromise the ability of the APS to continue to support the government and the Australian public to the highest standard," Senator Abetz said.

"We are asking our public service to look carefully at every position that becomes vacant and ask whether that position is really necessary; or whether there is a better way to do business."

But Community and Public Sector Union national secretary Nadine Flood said small-town Australia would feel the pain of Mr Abetz's decision.

"This decision is particularly tough on regional communities which have only a limited number of public sector employers in town," she said.

"If someone loses their job and can't be redeployed locally they'll be forced to leave town to find other work.

"We call on the government to change this new policy to allow agencies to fill vacant positions locally and guarantee regional jobs are not lost."