Federal government departments are poised to wage war on "dud" public servants in their ranks.

The Australian Taxation Office is leading the charge, pushing for changes to its "performance management" rules after taking action against just two alleged under-performers last year – from  a workforce of 23,000.

The government's biggest department, Human Services, is also moving to strip away legal workplace protections for bureaucrats at Centrelink, Medicare and the Child Support Agency regarded as "lower quality employees".

Unions say the moves will leave hardworking public servants hopelessly vulnerable to being unfairly targeted by their bosses.

But the departments say they are cutting red tape and making it easier to manage their workplaces in line with the expectations of the Abbott government.

Sparks flew in a meeting this month between ATO negotiators and unions in Canberra after Taxation officials dared utter the "d-word", a term that enrages both unions and the federal workplace authority, the Australian Public Service Commission.

The Taxation Office, as part of its new enterprise bargaining deal, wants to replace 99 lines of text on staff performance systems with just six lines.

The performance counselling guidelines will be stripped from one page to just four paragraphs and "unsatisfactory performance procedures" will also be "simplified".

The Australian Service Union told its ATO members that the intent of the bargaining position was clear; to make it easier and cheaper to sack public servants who had been branded by their bosses as underperformers.

The clear obligations and expectations of the ATO in these cases have been removed," union official Jeff Lapidos wrote in a bulletin to members.

"The ATO wants this change because it thinks it uneconomic to assist underperforming employees and it's much easier and cheaper to just rid get of them."

The ASU official also had words with Taxation executives after they brought up the term "duds" in the conversation.

Mr Lapidos asked that the "cringeworthy" word be replaced by "underperformer" instead.

Public Service Commissioner Stephen Sedgwick is also on record attacking media reporting that uses the term "duds", with the commissioner preferring the term "lower value employee".

At Human Services, executives want to move the department's underperformance procedures out of the department's enterprise agreement, where it is legally protected, and into regulations or policy where it can be watered-down or weakened.

The departments' moves are in line with the Abbott government's instructions to public service bosses for the current round of enterprise bargaining talks which is seeing 160,000 public servants covered by 117 agreements re-negotiate wages and conditions.

The government wants each public servant to have performance evaluations at least once a year examining professional performance and workplace behaviour.

The instructions also call for any "procedural or descriptive content" of performance management rules to be removed from the legal protections of enterprise bargaining agreements.

CPSU national secretary Nadine Flood said her union expected other departments and agencies across the Australian Public Service to follow the ATO and DHS in attacking underperformance procedures.

"The government is forcing agencies to remove a whole range of protections and the right to due process for workers who are facing the sack," Ms Flood said.

The union leader said that dwindling workforces in the public service meant that surviving worker were being "flogged" by bosses to keep up with punishing workloads and were in danger of losing vital rights and protections.