Labor will release on Wednesday economic analysis that it says will discredit the Coalition's claim that only 12,000 public service jobs would be lost under an Abbott government.
Finance Minister Penny Wong will reject the Coalition's estimate, made last Friday, that cutting those jobs would save $5 billion.
She will release costing undertaken by the Parliamentary Budget Office that indicates losing even 20,000 jobs by natural attrition in the first term of a Coalition government would save only $4.3 billion over the forward estimates.
The data will be released as a planned booster for Treasurer Chris Bowen, who faces off against his opposition counterpart, Joe Hockey, at the National Press Club on Wednesday. Mr Bowen will again challenge Mr Hockey to release the costings of the Coalition's policies.
Labor figures said the the Parliamentary Budget Office was asked to do the costing earlier this year, before the government increased the efficiency dividend. Labor says a Coalition government's hit on the public service of 12,000 jobs would come on top of the several thousand jobs to be lost under the higher efficiency dividend.
Last Friday, shadow assistant treasurer Mathias Cormann said economist Saul Eslake's assessment of the Coalition's costings and savings was wrong.
''Mr Eslake is not fully acquainted with all of our policy detail, our assumptions or indeed relevant Treasury data,'' Mr Cormann said.
''Our proposal to reduce the size of the public service by 12,000 - through natural attrition - has been costed by the Parliamentary Budget Office at about $5 billion over the forward estimates, not the $2 billion indicated by Mr Eslake.''
Labor officials stood by the government's result from the Parliamentary Budget Office that only $4.3 billion would be saved, even if the job losses rose to 20,000.
''This means Abbott will have to put front-line jobs in the gun,'' one official said. ''If these cuts were applied equally, this could mean around 8000 jobs would be cut from the ACT alone.
''Two in every five of these job cuts would occur in Canberra.''
On Tuesday, Canberra Liberals accused Labor Senator Kate Lundy of telling ''lies'' after a Fairfax Media analysis said she had made a false claim about the Coalition's policy on public service jobs.
A fact analysis was conducted on Senator Lundy's Twitter claim on Friday that the ''Libs have confirmed'' a cut of 20,000 jobs.
Mr Hockey has said 12,000 was a ''starting point''. Opposition Leader Tony Abbott said at his campaign launch on Sunday: ''We don't need 20,000 more public servants now than in 2007.''
On Monday, ACT Liberal Senate candidate Zed Seselja said: ''Senator Lundy has tried to shift focus away from her own broken promises on job cuts by spreading lies about the Coalition's policy.''
The Community and Public Sector Union called on the Coalition to guarantee it would not cut more than 12,000 public service positions, if elected.
National secretary Nadine Flood said Mr Seselja was trying to ''muddy the waters'' on public service numbers to divert attention from Mr Abbott's proposed cuts.
''One minute the Liberals are claiming the public service has grown by 20,000 under Labor, the next minute they want us to believe Labor have cut 10,000 public service jobs,'' she said. ''Sorry, Zed, you can't have it both ways.''