Workers at the giant Department of Human Services, which runs the agencies, will ignore their bosses' emails, screen their managers' calls, defy office rules on tea and toilet breaks and send messages to the public highlighting their dispute with management.

Public service dress codes may even be flouted in what has been dubbed the "DHS day of action".

Members of the public contacting the Medicare, Centrelink or Child Support Agency call centres will be told that any delays they have experienced getting through were due to the federal government cutting thousands of public service jobs.

But with the bureaucrats and their union wary of a public backlash, there are no plans to disrupt $150 billion in Centrelink payments and $29 billion which the department pays out each year through Medicare and the Pharmaceutical Benefits Scheme.

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Bosses say they are ready to hit back with "robust processes", threatening to dock wages of call-centre operators for the time it takes them to read a three-sentence message to a caller.

The Community and Public Sector Union, which has about 15,000 members among DHS 35,000-strong workforce, has secured a list of industrial actions that can be lawfully taken.

They include: internal emails carrying a message explaining how that staff member is on strike to "reject the Govt's low pay offer and cuts to rights"; not wearing the corporate uniform; call centre staff not inputting codes that inform management when they have taken or ended a call.

Protocols on meal or toilet breaks might be ignored and thousands of telephone operators will read a statement to callers saying: "Sorry if you've been kept waiting. The government has cut thousands of public service jobs for the past 10 years. DHS union members are fighting for safer workloads and better services for you."

But a spokesman for the department said his bosses were ready to handle whatever the union members threw at them.

"The department maintains local business continuity plans to effectively manage our day-to-day operations for a range of possible activities and interruptions, including protected industrial action," he said.

"The CPSU's proposed industrial action activities on December 11 are predominantly aimed at internal actions or administrative functions and are not expected to have a significant impact on our customers."

The spokesman warned that there may be consequences for workers participating in the day of action.

"If staff choose to read CPSU statements to customers and delay them doing their business with us, we will apply a partial work ban, which means not paying them for the period they read out the message.

"Industrial action on 2 and 3 December did not have an adverse impact on our customers, as we had in place contingency plans to address potential disruptions.

"The department is operating as usual, and we have robust processes in place to ensure industrial action does not affect the delivery of health and welfare payments."