The ATO's most hardline workplace union says it is prepared to agree in principle to a new draft enterprise agreement for the revenue agency's 19,000 public servants.

The decision by the Australian Services Union to tentatively endorse the terms of a new proposal from Tax Office bosses is likely to carry weight out of proportion to its several-hundred strong membership, given the union's tough approach to the dispute in the past.

A settlement at the ATO would add momentum to a growing push for peace in other departments where tens of thousand of public servants remain locked in a bitter industrial combat with the Coalition government, which has been raging since the early days of the Abbott-government.

ATO negotiators told the entire workforce on Thursday that they were sufficiently encouraged by the ASU's attitude to reinstate the online "enterprise agreement discussion" forum which was suspended two years ago as fury with a pay offer threatened to boil over and bosses pleaded for calm.

The Tax Office's main workplace union, the Community and Public Sector Union, which has a testy relationship with the ASU, is taking a much more cautious approach, saying it was "encouraged" by recent talks but a settlement remained a long way away.

The proposed deal is likely to carry average annual pay rises of 2 per cent for the the three-year agreement, but on the real sticking points, workplace rights and conditions, the ASU says ATO employees have much less to lose than under the previous three proposals, each of which was crushed in workplace ballots.

Union official Jeff Lapidos said he and his executive team would be prepared to give in-principle support to the new agreement if the pay offer, to a workforce whose wages have been frozen since 2013, was front-loaded and there was no major cuts to rights and conditions.

"We are confident that this can be achieved, even though the draft proposal for a new agreement has not yet been finalised," he said.

But any peace plan has a long way to go; the ASU's stance would have to be ratified by a vote of its members, a draft agreement, when produced, would have to be signed off by the industrial hardliner Public Service Commissioner John Lloyd, the attitude of the CPSU remains to be seen and the whole deal would have to be voted up in an all-staff ballot.

CPSU Deputy Secretary Melissa Donnelly was cautious in her response to the ASU's announcement.

"The last offer from ATO management was soundly rejected just four months ago by 71 per cent of staff, so real progress has to be made for a majority of staff to want to support the agreement," Ms Donnelly said.

"We're in exploratory discussions with the ATO to find a way forward in this messy and protracted dispute.

"We have been somewhat encouraged by the tone and content of recent discussions, but there is still some way to go and ATO are yet put forward a new proposal."

"CPSU members working in Tax continue to tell us that they want an agreement that is fair and reasonable and doesn't strip away rights and conditions."