Labor Senator Helen Polley questioned NDIA chief executive Martin Hoffman about a recently released FOI which disclosed that the uppermost levels of the agency's workforce was full of labour hire workers.

She questioned Mr Hoffman about whether this meant the agency had breached the Public Service Act which has a provision that SES level staff are to be employed under the act. She also asked whether this met the public service's principles of merit-based and equal opportunity employment.

Mr Hoffman indicated that all SES level contractors were subject to the APS Act as they had been approved and granted delegations by the Public Service Commissioner.

The FOI document showed that as at September 18, the agency employed 22 contractors at SES level and 214 in EL2 positions.

One of the SES positions filled via labour hire was the business manager in charge of procurement, meaning the executive in charge of making labour hire decisions is themselves a labour hire employee.

The chief information officer, chief counsel and several general managers were also labour hire appointments.

Mr Hoffman told the estimates hearing that the NDIA had 56 SES level positions and the 22 contractors represented a significant drop from this time last year when 34 contractors filled SES positions.

He said the agency intended to have fewer than 21 by Christmas.

"[The number of contractors] reflects a program that has been in place since the agency started," Mr Hoffman said.

"It reflects the need to rapidly stand up a brand new agency doing a world first program at this scale, giving the flexibility to bring in the sort of experience and skills that are needed."

CPSU deputy secretary Beth Vincent-Pietsch said the revelations had "blown a hole" in Finance Minister Mathias Cormann's evidence before estimates last week.

"Minister Cormann said labour hire and external suppliers were only for short term needs or specialised skills. The NDIA evidence has blown this out of the water," she said.

"This evidence shows the ASL cap is having deep and worrying impacts at every level of the APS, from service delivery to the highest levels of the executive.

"That means that we have multinational organisations profiting off the NDIS instead of focusing resources on outcomes for participants and their families."

She again called on the government to lift the ASL cap on agencies such as the NDIA to allow funds to be spent on APS employees and their work.

Mr Hoffman admitted in estimates that the agency bore extra costs by using contractors to cover fees for labour hire companies, but took on notice to provide an exact cost breakdown.

He said it was also possible some of the SES level contractors would earn more money than the normal SES band staff. But he said all contractors were paid in line with the remuneration policy set by the board.

"They are employed consistent with board approval through the people and remuneration committee to ensure we are making decisions in the interests of the agency," Mr Hoffman said.