CPSU National Secretary Nadine Flood.

CPSU National Secretary Nadine Flood. Photo: Supplied

Unions have lashed as "ludicrous" claims by the Abbott government that a push for a 12 per cent pay rise for federal public servants over three years could cost the jobs of more than 23,000 bureaucrats.

Internal government modelling obtained by Fairfax Media last week showed the wage claim could add an extra $1.9 billion to the taxpayer funded payroll, a trend Public Service Minister Eric Abetz called unsustainable.

Community and Public Sector Union national secretary Nadine Flood said cutting 23,460 jobs would represent about 14 per cent of the nation's 165,000 federal public servants.

"It is just ludicrous to suggest that a 4 per cent pay rise would lead to such large cuts," she said.

“The government hasn’t shared this modelling with unions, government agencies or workers, choosing instead to give it directly to the media.

"It is pretty obvious the figures have been cooked up to provide cover for a government intent on making more wide-scale cuts to jobs and services.”

Ms Flood said the Abbott government was blaming wages and conditions as the source of all problems in the Australian economy.

She called on the government to engage in constructive wage negotiations and not "bomb-throwing".

Treasurer Joe Hockey warned households and business last week that Australia had reached the end of its ''age of entitlement''.

Mr Hockey's comments were interpreted as further positioning by the government ahead of an austere federal budget, to be handed down in May.

A senior government source told Fairfax on Friday there was ''no way we are borrowing from overseas to fund public servants' pay increases'', suggesting a looming fight over the wage claim.

The union called for guaranteed wage rises of 4 per cent each year, double the rate of inflation forecast for 2014-15 in the mid-year budget update released in December.

Ms Flood said public sector workers would be dismayed by the comments.

“Senator Abetz has effectively shut the door on mums working in Centrelink, hardworking Border and Customs agents and the thousands of other public servants who’ve been ready to sit around the table and bargain in good faith to hammer out a reasonable deal,” she said.

The Public Service Commission calculated each increase of half a per cent a year would grow the public service wage bill by $78 million, and paying the full claim would cost $1.9 billion over three years.

Senator Abetz said most Australians would agree the increase was not sustainable.