Up to 300 applicants are fighting for each public service job vacancy in Canberra and the main public sector union says more than 5000 job cuts have been announced since the Abbott government took office.

Community and Public Sector Union national secretary Nadine Flood told a parliamentary committee in Melbourne on Thursday that her union's official casualty count had just topped 5050 positions, and that much worse was expected.

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The true toll will be much higher with most discarded temps and contractors, numbering into the thousands, not counted in the union's official figures.

Canberra job seekers report that they are up against 250 to 300 other applicants for each of the small number of vacancies in the capital.

Public Service Minister Eric Abetz has consistently said the rising number of redundancies in the Commonwealth bureaucracy are the direct result of years of Labor-imposed efficiency dividends on agency and department budgets, a claim disputed by the ALP.

Mr Abetz's office did not respond on Thursday to requests for comment.

Ms Flood told the Senate select committee inquiring into the government's Commission of Audit that the strain was showing on the public servants who still had their jobs and on the services they were hired to deliver.

''Our figures, as at the end of last week, just tipped over 5000, with areas such as the Department of Communications and others,'' Ms Flood told the hearing. ''In general, that does not include not renewing the contracts of non-ongoing staff.''

The figures had been compiled from confirmed job losses where agencies had notified the union in writing of specific numbers, she said.

''There is a larger scope of agencies talking about 'we will need to cut jobs but we're not sure how many' and it will depend on the Commission of Audit and the federal government,'' Ms Flood said.

Damage to the nation's welfare systems as well as the Australia's bio-security border controls were examples of cuts to the bureaucracy's ability to do its job, she said, as well as mental health problems emerging among surviving public servants.

Citing as an example the bureaucracy's largest department, Human Services, the union claimed DHS had lost up to 5000 staff since 2009 and pressure on the services it delivered - Centrelink, Medicare and the Child Support Agency - was rising.

''In the last year alone, the number of calls to Centrelink and Medicare rose by 1 million alone, so we have far less employees doing far more work,'' Ms Flood said.

''It doesn't take a brain surgeon to figure out that that creates real pressures, those pressures are substantial for employees, substantial for clients who are waiting for payments, waiting for help.''

The Canberra Times revealed last week that 340 of the Agriculture Department's 2000 border security workers wanted to quit their jobs. Ms Flood told the committee fault lines were emerging in the department's workplaces across Australia.

''Our members are raising serious concerns that the budget pressures in the department 's quarantine program actually means there are major bio-security risks which mean you could let pests and problems into Australia that have an enormous impact on Australia's agricultural industry, cost government billions for the sake of a relatively small expenditure on public services,'' Ms Flood said.