The Australian Services Union says so many tax officers are now working above their pay scale in the ATO's Large Business and International (LBI) division, it is making a "charade" out of the voluntary tax compliance system.

The row is the latest dispute between the Tax Office and its workforce that is heading towards a showdown in Fair Work Australia (FWA) as the union accuses the ATO of throwing inexperienced staff in at the deep end in an effort to cut costs.

But the department says that work is being allocated according to approved public service guidelines.

LBI embarked on its restructure in the second half of 2012 with 56 executives, all above the Executive Level 1 (EL1) pay grade, identified as "excess".

Workers were advised this month to expect more redundancies, this time in the senior ranks of the LBI division's risk strategy section.

But the union is preparing a case for FWA where it will argue that that ATO is filling the gaps with more junior staff who are not ready to match their skills against highly paid tax advisers hired by large Australian and overseas corporations.

"The ATO is trying to cut costs by having work done at lower classification levels than we would expect given the complexity and responsibility of the work," ASU Tax Office organiser Jeff Lapidos said.

"LBI is the stand-out in this. The EL2s are being expected to undertake the work of the Senior Executive Service (SES)."

Mr Lapidos said it was the most senior tax officers who should handle the highest-level and most complex corporate work.

"We expect the Senior Executive Service in LBI to be able to match wits and expertise with their clients' tax managers and representatives," the union official said.

"The work is being pushed down to become someone else's problem…

"Voluntary compliance is becoming a charade of going through the motions of being a good corporate citizen."

The union will also allege that some senior officers have been pressured into taking redundancies.

But an ATO spokeswoman said the office was compliant with Australian Public Service (APS) approved guidelines for work levels, that staff had been consulted about the shake-up in the Large Business and International division and that there had been no forced redundancies.

"We continue to comply with the APS employment framework, including work level standards, to ensure the work requirements for all our staff at any classification align with the duties to be performed," the spokeswoman said.

"Over the past year, LBI has reviewed a number of its functional areas and, as a result, made changes to its structures and processes.

"During these reviews we have worked with affected staff and employee representatives by providing them with information and opportunities for consultation''.

There have been no forced redundancies due to the reviews, she said.