Services Australia workers are being forced into the office despite lockdown orders, the Community and Public Service Union has claimed.
The union said managers were telling workers in Brisbane, Sydney, Perth and Darwin to come into work in non-essential and non-customer-facing roles, such as processing staff.
CPSU said these employees could work from home.
The four cities have been in lockdown while the country tries to maintain the spread of the Delta variant of COVID-19.
Lockdown rules in each city stipulate people must work from home if they can.
Workers have also been told to use their own leave when identified as a close contact, the union claimed.
Services Australia said they are following the relevant advice from state and territory authorities.
"Throughout the pandemic, staff have continued to work safely from the office, and we have facilitated work from home," said Services Australia General Manager Hank Jongen.
"We enable those staff who can work remotely to do so while continuing to deliver essential services."
CPSU president Alistair Waters said staff should be working remotely.
"Workers get that the work they do is essential but when they can do that work from home they should be working from home," he said.
"It's not good enough, and Services Australia needs to explain why they think they are above the national and state health advice."
The CPSU said managers were making the orders and it did not reflect an organisation-wide policy.
"This is not our first lockdown. It is indefensible for the agency not to have a clear contingency plan for local outbreaks. It is allowing local managers to wilfully and dangerously ignore lockdown orders," Mr Waters said.
The union said they were notifying a dispute under national Workplace Health and Safety laws.
Services Australia said they would "closely monitor staff welfare and adapt within the rapidly changing situation."
"Where staff members are in the high risk category, or who live with someone in this category, arrangements are made available so their work can be done from home, including call and processing work," said Mr Jongen.