Bosses at the Civil Aviation Safety Authority want their public servants at their desks for an extra 45 minutes each week in return for a 2 per cent pay rise.

CASA's chief executive says the offer is all the agency can afford right now but has assured his 830-strong workforce that their conditions and entitlements are safe.

The new proposal at CASA comes as the massive Defence Department moves closer to a vote of its 20,000 public servants on a new wage deal and the Australian Taxation Office prepare for fresh negotiations in the wake of the crushing defeat of a proposed enterprise agreement

CASA's Chief Executive Mark Skidmore told the authority's staff last month that the authority is so short of money, it had to approach the wage talks with an eye to its future financial viability.

"You are also aware that CASA is operating in an extremely challenging budgetary situation and we have been required to address this in the context of the EA remuneration affordability so that CASA has a sustainable future," Mr Skidmore wrote to his workers

"...to make this work, this new offer does include a small increase in working hours.

"It is proposed that we increase our working hours by 9 minutes a day from 7 hours and 21 minutes to 7 hours 30 minutes daily."

Mr Skidmore said the proposed new hours, which would begin in 2018, the last year of the three-year agreement, would bring CASA into line with the rest of the public service and with "community expectations".

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The chief executive said the extra work was the only change to entitlements in the proposed EA and that the offer did not come at the price of job cuts, as had been proposed to fund offers to other departments and agencies.

But technical union Professionals Australia says its members at CASA, where workers have not had a pay rise since mid-2013, are unimpressed with the proposed deal, saying the agency was trying to "get blood out of a stone".

"Members don't think this is anywhere near a fair pay offer with no comprehension of government-caused delays and a clear move to sever the link between the agreement and relevant employment policies making such conditions close to unenforceable and easier to change," union official Dave Smith said.

"If CASA's capacity to have a sustainable workforce is threatened then the Australian community should be concerned and the Government should ensure they are funded appropriately.

"They shouldn't have to rely on getting 9 minutes a day more blood out of the stone."

Meantime, the Defence Department looks set to go to a vote in February or March on its new enterprise agreement with workplace unions reporting little progress in trying to tweak key aspects of the proposed agreement.

The tax office will sit down again with unions on Monday to try to pick up the pieces after the 85 to 15 per cent defeat of its wage proposal.

Initial progress is expected to be slow with the ATO understood to want a survey of its employees carried out, to determine the reasons behind December's crushing no vote, before it puts together a fresh proposal.