More than 1000 St John Ambulance officers nationwide have issued a 14-day notice of industrial action.
The First Union says the planned strike comes after an attempt by St John to squeeze more out of already stretched front-line staff.
The union's ambulance professionals co-ordinator, Lynette Blacklaws, says the officers will continue to respond to call-outs.
Their industrial action would include a ban on paperwork, disrupting St John's ability to invoice patients.
Ms Blacklaws says the strike is for the safety of staff and their patients.
"We are seeking solutions to issues that cause dangerous fatigue, such as not receiving rest and meal breaks coupled with an increased workload," she said.
St John human resources director Tom Dodd said the organisation had just received notification from the five unions representing staff and was considering it.
He said St John was in the middle of collective bargaining with the unions and had agreed to mediation before the notification was issued.
"We continue to work in good faith and discuss relevant issues directly with unions and our staff," he said.
The notice came on the eve of a 48-hour strike by junior doctors over roster hours they say are unsafe.