Government Services Minister Bill Shorten announced a $228 million boost for Services Australia in November 2023.

The money has funded 3000 jobs at the agency, which delivers key programs including Centrelink and Medicare.

Mr Shorten's announcement followed an admission from a top official at Senate estimates that the agency wasn't meeting its "own KPIs" on customer service performance.

But the Community and Public Sector Union wants the government to ensure additional funding for the positions is ongoing.

"One of our key concerns at this point in time is to ensure that the recently announced Services Australia jobs have ongoing funding," CPSU national secretary Melissa Donnelly said.

"The jobs that were announced late last year are making a difference in terms of addressing the backlog and the workload pressures that exist in that agency, but we want to make sure that continues into the future."

The union's pre-budget submission says the new jobs should not be treated as a "one-off stop gap, but an ongoing investment in the capacity of Services Australia".

"Unfortunately, Services Australia often has one-off budget supplementations that do not provide the agency, employees or the public with certainty."

It pointed to investments made in the Albanese government's first two budgets, which modelled this "trend" - including a $588.4 million funding injection for disaster response in 2022-23, which was topped up by $231.8 million in 2023-24.

Mr Shorten said that while the government was committed to resourcing Services Australia, he could not comment on budget matters.

"The Albanese government is committed to ensuring government services are delivered in a convenient, secure and efficient way, but to achieve this Services Australia must be properly resourced to do so," Mr Shorten said in a statement.

He said onboarding the 3000 new starters had been the agency's "fastest ever recruitment of permanent staff on this scale".

"The union knows I am unable to comment on the budget until it is delivered on May 14, but I am sure the offices of the Treasurer and the Finance Minister welcomed its submission."

The CPSU was left disappointed after the May 2023 budget, when roles at Services Australia dropped by 1800, while most other government agencies saw an increase.

Then-agency head Rebecca Skinner told staff these roles had been part of a COVID-19 surge, and the staffing level was "normalising to pre-pandemic levels".

The CPSU's budget submission highlighted that staffing levels at Services Australia - formerly the Department of Human Services - were still well below what they were a decade ago.

While the agency's average staffing level was about 30,089 in the 2013-14 financial year, that figure had fallen to 26,692 for the 2023-24 year.

Average staffing level represents the average number of full-time equivalent staff in the agency, as opposed to an overall headcount.

Both Labor and the Coalition have criticised each other for the agency's shrinking resources.

Mr Shorten claimed the "former Liberal government deliberately under-funded, under-staffed and sabotaged Services Australia and its predecessor department [the Department of Human Services]".

He pointed to falling staffing levels in the past decade - most of which has occurred under Coalition governments.

In 2015, the Abbott government sought to tie the size of the federal public service to the 2006-07 level of 167,596.

This measure - referred to as the ASL cap by Labor - led to agencies instead relying heavily on contractors, consultants and labour hire.

But the opposition's spokesperson for government services, Paul Fletcher, claimed Mr Shorten was "a hypocrite when it comes to staffing decisions", pointing to the staffing drop at the last federal budget.

"There's no certainty around the funding of these 3000 jobs because Labor only provisioned funding until 30 June 2024," he said of the $228 million investment.

Mr Fletcher also criticised a decision to axe a contract with Serco in June 2023, which represented 600 call centre workers, linking this to an "unacceptable surge in call wait times".

The move is in line with the government's efforts to reduce reliance on third parties, after it was revealed that the Morrison government spent nearly $21 billion on an external workforce in the 2021-22 financial year.

Correction: An earlier version of this article contained an incorrect amount that Services Australia received in November 2023. It received $228 million.