The Federal Government has revealed its plans to rein in public service recruitment and cut 12,000 positions.

Prior to the 2013 election, the Coalition promised to reduce the federal public service through natural attrition, including retirement.

Minister Assisting the Prime Minister for the Public Service, Senator Eric Abetz has announced interim recruiting arrangements which will help the government meet the target.

Under the new system external advertising of vacancies and temporary jobs will be limited to critical vacancies, or positions which require specialist skills.

It means jobs will still be advertised inside the public service, unless someone with the correct skills can not be found internally.

But the government says it will continue to offer recruitment programs for course graduates and Indigenous employees.

Minister Abetz says the changes are important to reduce unnecessary spending.

"We went to the Australian people promising to improve the former Labor government's parlous budgetary position and this necessitates a reduction in the size of the public service," he 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."

Community and Public Sector Union (CPSU) national secretary Nadine Flood says the changes will move existing public servants into vacant jobs, leaving gaps elsewhere.

"The government can try and dress it up any way they like but this is simply a massive staff cut," she said.

"We are calling on the government to confirm that they will stick by their election promise not to cut more than 12,000 jobs.

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

"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."

The union says the changes are likely to lead to customer and service delays.

"This policy is a recipe for widespread delays and queues and it will hit every agency, from the Tax Office and Human Services to Customs and the Bureau of Meteorology," Ms Flood said.

"From today agencies will be forced to cope with dwindling staff numbers rather than providing vital services to the public and quality advice to the government."

The Australian Public Service Commission (APSC) will begin implementing the new arrangements.