The ATO looks set to offer its 18,000 public servants a 1.5 per cent pay rise, following several small public servants departments and agencies who have struck deals with their workforces at that figure.
But unions are trying to get out in front of the Tax Office's bosses, already urging their members to vote "no" to the deal if it contains a long list of cuts to entitlements and conditions put forward in the last offer.
But the Tax Office would not be drawn on Monday about its new proposal, simply confirming that it was working towards putting a new deal to its workforce.
The ATO is due to unveil its offer soon and the slight relaxation of the Abbott government's tough public sector bargaining policy is expected to allow a 1.5 per cent payrise, a big improvement on the .8 per cent offered in February which provoked a backlash in workplaces around Australia.
The much-anticipated offer at Tax could open a new front in the industrial unrest that is now affecting much of the public service with workplace union the CPSU already gearing up for a fight at the ATO.
Members were told in a bulletin on Monday that a 1.5 per cent pay rise was "a pay cut in real terms" with the union predicting the coming offer would contain many of the tough conditions contained in the last proposal.
"It is likely the offer will include the same cuts to conditions and rights as the last offer, with changes only at the margin," the bulletin stated.
"As it stands, the status quo is already a better deal."
Union members were issued with a long list of workplace entitlements that the CPSU said were still on the chopping block in a clear sign the new proposal, when it is unveiled, will meet opposition.
"These cuts to rights and conditions have already been proposed by the ATO, cutting over 100 years of progress by members in the ATO.
"These conditions make the ATO a good place to work."
An ATO spokeswoman said the office was working towards making an offer and had begun to set up meetings with unions to begin the process.
"The ATO is seeking final approvals for its pay offer," she said.
"In anticipation of this, we have contacted bargaining representatives for their availability to recommence bargaining in the coming week."
Nine enterprise agreements have now been voted up under the government's bargaining policy: three at NBN Co, and one each at Comsuper, the Australian Office of Financial Management, Treasury, the Australian Public Service Commission, the Australian Transport Safety Bureau and Communications.
Most of the agreements that have been accepted have contained pay rises at or close to 4.5 per cent over three year.
But big challenges remain with none of the large service delivery agencies like the ATO or the Department of Human Services, where many of the of the public service's "frontline" staff work, having reached agreement.
Immigration and Border Force officers caused disruption at international airports on Monday with industrial action as part of their dispute with quarantine and bio-security workers from the Agriculture Department joining in.
There has been low level action at Human Services but major disruptions to Centrelink or Medicare have yet to materialise.
DHS has boosted a pay offer in July to its 35,000 public servants to 1.5 per cent and backed down on some tough bargaining conditions in a fresh bid to settle its ongoing wage dispute.