Public servants in the Defence Department walked off their “safety-critical” to protest the long-running public service pay dispute drags on.

Civilian technical officers at two RAAF bases in NSW, a Navy airfield and an explosives testing range walked off the job, saying it was the only thing they could do to draw attention to the government's “draconian bargaining policies”.

But the department has moved to play down the action, pointing out that it consisted of just four workers.

The union for the workers said each of the technicians played a vital safety role, and that the strike would be effective in slowing the work of the already diminished Defence Department.

The department is expected to sit down with unions in the coming days for more talks, continuing two-and-a-half years of negotiations depriving public servants of any pay rise.

The NSW-based technicians on strike this week are members of the Australian Manufacturing Workers Union, at RAAF Base Williamtown, RAAF Base Richmond, HMAS Albatross in Nowra, and Defence Establishment Orchard Hills.

The union says one of its concerns is about the number of technical maintenance jobs filled by staff that have been shifted over from other Defence Force positions, rather than experienced workers.

But the stymied pay dispute remains the biggest hitch.

“The technical workforce in Defence is being run down, so there's not a lot of them and some of them are members of other unions,” AMWU assistant national secretary Mike Nicolaides has told Fairfax reporters.

“They [the technical officers] maintain the navigational aids and if the navigational aids go down, the facility becomes non-operational.

“They're in critical positions.”

“These people are required to give five days notice of industrial action instead of the normal three because they are in safety-critical areas.

“Because of that, we have been reluctant for them to take industrial action, and the industrial action that we have taken has been done on far greater notice, so we've given Defence sufficient notice so they can make alternative arrangements.

“Now of course that's inconvenient, but we don't want to threaten safety.”

A spokesperson for the Defence Department said the strike would have “minimal” impact.

“At the time of this advice four employees have been reported as participating in the notified industrial action,” she said.

“Industrial action has had minimal impact on operations.”

The pay deal expected to be tabled in the next round of talks offers a raise of 3 per cent in the first year, then 2 per cent and 1 per cent in the following two years.

The civilian workforce still has some lingering outrage at cuts to conditions to entitlements in the offer, but insiders say they are most offended by the big concessions made to colleagues in the Australian Defence Force last year.

Government negotiators were seen to bend to the public backlash at the low-ball offer given to non-civilian ADF staff, while the civilians (often working in the same office) are given far less generous offers.

Mr Nicolaides said more industrial action is likely.

“Each of these Defence establishments is basically different from the next in term of funding, the level of union membership and other things,” he said.

“It's dependent on the circumstances of each site, whether something will happen and that will vary from site to site.”