The result marks the first time in the public service's two-year industrial battle that a workforce has voted three times to reject an agreement, an occurrence thought to be unprecedented in the history of the Australian Public Service.

The failure of yet another proposal means departmental staff undertaking bio-security duties at Australia's air and sea ports will join public servants from other departments and strike next week.

In another desperately close result, Agriculture's latest proposal was defeated by just 111 votes – a margin of 51 per cent to 49 per cent, with 3897 votes cast and an 86 per cent turnout.

The department's senior leadership had been widely expected to get its offer over the line at the third time of asking after a huge campaigning effort and an unusual intervention by departmental secretary Daryl Quinlivan last week.

But the latest result, announced to staff on Tuesday morning, is an increased no-vote from the 62-vote margin recorded in December, with an increased turnout, and will leave the department's bosses wondering where they go from here.

The department had little to say through official channels on Tuesday.

"The department is considering its next steps," a spokesperson said in a statement.

The result will be keenly observed in the giant Defence Department, which is set to emulate Agriculture's approach and go to a quick repeat ballot with a near identical offer after its own proposed agreement went down this month by just 1.8 per cent, or 249 votes.

Agriculture's main workplace union, the CPSU, said the result opened the way for the department's public servants working on quarantine and other border duties at air and sea ports around the country to join in the mass strike action planned for Easter week.

"This no vote in Agriculture is the first time during this protracted dispute that a major agency's offer has been rejected by staff three times," union leader Nadine Flood said.

"CPSU members in Agriculture are now preparing to join next week's mass strike action across government agencies and international airports."

The union flew workplace representatives from field operations around the country to Canberra to campaign for a no-vote, in an effort it dubbed "Operation Flouro", to try to match the marketing blitz mounted by Agriculture.

Mr Quinlivan told his staff on Thursday that a yes vote would give managers the power, under the new agreement, they needed to deal with the minority of public servants who were rorting their personal leave entitlements.

Another workplace union, Professionals Australia, said the result was a rejection of "cynical" tactic by the department.

"The result is a rejection of cynical attempts to try and rerun votes on largely the same agreement offer until [it is] successful," union official Dave Smith said.

"Agriculture needs to now properly listen to [its] workforce.

"[It needs] to drop [its] proposals for veterinary officers and change [its] approach to the stripping of workplace rights and conditions."