Staff at the Australian Tax Office (ATO) have been offered 500 voluntary redundancies as the department looks to shed 900 positions.

The ABC has confirmed that ATO second commissioner Geoff Leeper has sent an email to all staff, calling for expressions of interest for a voluntary redundancy program.

It is understood the organisation has funding for around 500 voluntary redundancy packages. Priority will be given to staff working in areas which there is believed to be duplication of effort.

The ATO says only superfluous positions will go and no services will be affected as it plans to reduce staff numbers by 900 over the coming months.

Mr Leeper said the call was driven by the need to meet budgetary targets.

"Last year, the commissioner advised we need to work hard to achieve a balanced budget in 2013-14 and beyond," he said in the email.

"This will help reach our estimated workforce reduction target of 900 full-time equivalent employees...and position our workforce for the future."

Alistair Waters from the Community and Public Sector union says they will be watching developments closely.

"We are going to be working with the Tax Office to make sure that this process is entirely voluntary and that nobody is forced to lose their job," he said.

The ATO says with more than 25,000 staff it expects to have no problems achieving the redundancies.

The redundancy program is expected to be finalised by June.