Two-thirds of staff at Prime Minister and Cabinet have again rejected a pay deal described as "harsh and unfair" by the public service union.
The high-stakes vote in Malcolm Turnbull's department is the latest blow to the federal government's public service bargaining policy.
The workers had been offered a "measly" pay offer of 5.5 per cent over three years, the Community and Public Sector Union said on Sunday afternoon.
The no vote was an emphatic refusal to accept Mr Turnbull's public sector bargaining policy, the union said.
It reported 74 per cent of staff cast a vote in the ballot, which closed on Friday, with 68 per cent voting No.
The news follows no votes at the Electoral Commission, National Archives and the Australian War Memorial, while the Employment Department voted yes and the Australian Sports Commission returned a landslide approval for its new deal.
Since an earlier wage proposal was rejected at PM&C in a ballot late last year, the union had been campaigning hard for a no vote and was confident of the result.
The prime minister's office was contacted on Sunday for comment on the latest result.
CPSU National Secretary Nadine Flood said the staff were not willing to accept a deal that would have stripped important rights and conditions, either outright or by moving them into unenforceable policy.
The pay offer did not match the 6 per cent over three years being offered across much of the APS, while slashing rights and conditions, she said.
The offer had been only marginally improved since being rejected in October last year and again offered no compensation for the more than 18 months staff have gone without a pay rise, Ms Flood said.
"Prime Minister and Cabinet is an agency that has a strong history and culture of backing government bargaining policy, so two strong no votes in five months is a stunning rejection of Prime Minister Malcolm Turnbull's public sector bargaining policy from his own staff," she said.
"Just as is the case across scores of agencies, many of the conditions that the mums and dads who work in PM&C are fighting to save are what makes it possible for them to balance work with their family commitments.
"They know, as Public Service Commissioner John Lloyd has admitted, that conditions taken out of agreements and moved into policy can be arbitrarily changed or removed down the track."
Ms Flood said many of the staff who have been shifted to PM&C from Indigenous Affairs were particularly unhappy with what was being put on the table.
"These are extremely committed and professional staff and they weren't willing to lose their hard-fought conditions," she said.
"Tens of thousands of staff have voted to reject these dud deals, including the recent 79.5 per cent no vote in the largest Commonwealth agency, the Department of Human Services.
"The message has been just as emphatic at other major agencies, with 85 per cent voting no in the Tax Office and 91 per cent no in the Department of Immigration and Border Protection.
"Prime Minister Malcolm Turnbull has an opportunity to listen to the strong message that he has been given by the people who work in his own department."