Staff at the Department of Human Services have been warned they will not get a better offer than the one they rejected last month.

DHS has told its 34,000 employees that the “considerable concessions” already made during negotiations were as much as it could do.

Agency heads also pointed out that other departments that managed to agree to offers comparable to the one DHS staff rejected.

Meanwhile, Defence and the ATO are expected to reject their latest proposed agreements as well.

DHS senior executive Adrian Hudson accused the CPSU of immutable stubbornness in a memo to staff this week.

“During bargaining the department has made considerable concessions, however the CPSU has not,” Mr Hudson said.

“Bargaining is not a one-way street and all parties must be prepared to give and take.

“In February 2016 we gave you our best offer – staying within the requirements of the bargaining framework while ensuring that the offer was affordable.

“The proposed agreement included the highest available pay offer under the bargaining framework and was above the current inflation rate of 1.7 per cent.

“It also retained most of the entitlements from the current agreement.”

While much of the APS have been victims of an effective wage freeze as the negotiations drag on, Mr Hudson says there will be no back pay or compensation.

“The proposal could not include back pay,” he wrote.

“This was in line with the bargaining policy, which states; 'Remuneration increases are to apply prospectively'.

“Such requirements are not new; they have been a feature of bargaining policies of successive governments over many years.

“Several other departments, including Health, Social Services, Veterans' Affairs and Employment, have all recently voted to support agreements.

“Our offer was equal to or better than all of those offers.”