Staff in a federal department supplying front line services will go on strike tomorrow in protest over their pay offer.

As well, civilian staff in Defence have made the decision to strike if necessary as industrial action across the public service escalates.

The two-hour stoppage tomorrow by union members in the Department of Agriculture, Fisheries and Forestry could disrupt quarantine inspections at airports and meat inspections at abattoirs.

The Community and Public Sector Union's national secretary Nadine Flood said civilian workers in Defence had voted in favour of protected industrial action.

"This is the first time in more than 20 years that civilian staff in Defence have voted to take industrial action over bargaining," Ms Flood said last night.

"The decision of CPSU members is in a sense historic and it reflects the growing levels of frustration across the public service.

"That vote means more than 75,000 staff work in departments and agencies that have rejected their enterprise agreements."

Defence staff will not take immediate industrial action, pending the outcome of next weeks talks.

A recent vote in Customs and Immigration drew ballots from less than 50 per cent of union members, making them invalid.

New ballots are being held in those departments, with the union trying to ensure that ballots reach staff on time in far-flung posts including detention camps.

The union said it was frustrated that all of its productivity proposals had been rejected.

"Our members in [Department of Agriculture, Fisheries and Forestry] don't want to disrupt the services they provide but they accept there will be some impact," Ms Flood said.

"Employees across the public service are becoming increasingly frustrated that the Public Service Commission and the Government are blocking genuinely negotiated settlements to bargaining. Agency managements and unions are sitting at the bargaining table but our capacity to reach sensible solutions is being limited by the restrictions put in place by the Public Service Commission and the Government.

"I think more than 75,000 public servants in agencies that have rejected agreements sends a clear message to the Government that something is wrong.

"These are reasonable people and we should not be looking at industrial action in an increasing number of agencies because there appears to be no willingness to settle these agreements."

Ms Flood said civilian staff in Defence were making sensible changes to deliver better services.

"Those productivity gains should be recognised in bargaining," she said.