The Federal Government's largest department has been offered a wages deal that is substantially below inflation and would require public servants to forfeit conditions.

Under the proposal, the best possible outcome the 30,000 employees of the Department of Human Services can expect would be a pay rise of just over 1 per cent per year.

Workers have been offered a pay rise of just 1.5 per cent a year, but staff were told if the deal was not finalised by September it would drop to just 0.75 per cent.

Inflation is currently running at 3 per cent per annum.

DHS is hoping its staff will be able to vote on the new pay offer within the next two weeks, bypassing the union.

Under the Federal Government's tough new bargaining approach, cash-strapped agencies have to fund any new pay rises through their existing budgets.

DHS General Manager Hank Jongen said it was important to understand that for every dollar that was put forward as a salary offer, real productivity gains had to be found.

That means workers at Centrelink, Medicare and the Child Support Agency would be behind their desks for an extra six minutes every day.

"We are not asking our staff to sacrifice annual leave, it is true that the agreement allows for an additional six minutes a day but we believe that that's not unreasonable," Mr Jongen said.

Federal Secretary of the Public Sector Union the Nadine Flood said the offer was ugly.

"What we are seeing is ordinary working mums in Centrelink and Medicare being asked to cop cuts to their rights, cuts to their conditions, changes to their hours and all in return for a pay rise of 0.75 per cent a year, less than one per cent," she said.