Ahead of a ballot of the department's 19,000 public servants that begins on Thursday, the department has blitzed its workforce with 51 separate "bargaining bulletins" and 98 staff meetings.

Workers are being greeted with on-screen marketing material urging a Yes-vote when they log onto their computers each morning and the department's boss, Dennis Richardson, appeared in a presidential-style video address to the workforce on Tuesday .

The department is seeking to hammer home a simple message.

"You will receive a pay rise of 6 per cent over the next three years and your conditions of employment will be maintained," the on-screen message states.

"All APS (Australian Public Service) employees should get the facts and make an informed decision."

But workplace unions disagree as they make their case for a No-vote, arguing entitlements and conditions are to be lost as large swathes of the Defence enterprise agreement are stripped out and moved into policy.

Technical union Professionals Australia has cried foul over the campaign, saying it has not been allowed to hold meetings on work time to put its case to workers.

"You don't hold close to a hundred, tightly managed briefings and issue 50 bargaining bulletins to all staff and deny such facilities to employee bargaining representatives unless you have a very poor offer to sell,' union official Dave Smith said.

"It's like a bad pyramid selling scheme.

"Defence employees can see through this snowstorm of propaganda and they are sick of the waste of resources on this process that is providing a poor pay outcome while cutting critical workplace rights and conditions."

Meantime, senior officials at the Australian War memorial in Canberra have gone back to the drawing board in an effort to understand their wage offer fell flat in a recent ballot.

Staff rejected the now-standard offer of 2 per cent per year for a three-year deal by a margin of 53 to 47 per cent even after the memorial's management had sweetened the deal in line with the government's softened bargaining policy.

Chief finance officer Leanne Patterson said she would be running "small consultations" with the AWM's staff in a bid to determine what went wrong.

"Answers to questions raised and information gathered will then be made available to all staff, and will inform the senior management team in determining the most appropriate way forward with the proposed agreement in the best interests of the memorial and its staff," Ms Patterson told workers in an email.

In another development, staff at the National Archives of Australia have formally rejected an enterprise agreement for the first time in the agency's history, with nearly 70 per cent voting no to a 2 per cent a year offer, with 80 per cent of the institution's 430 eligible staff casting votes.

The Community and Public Sector Union says archives workers rejected a deal that would have stripped important rights and conditions in return for a poor pay offer that did not compensate workers for a wage freeze that has now stretched for more than 18 months.

Correction: An earlier version of this story incorrectly stated that Defence's EA ballot begins next week. Voting begins on Thursday.