The Australian Salaried Medical Officers' Federation on Wednesday said it would continue three days of planned industrial action beginning next week, in the face of an industrial court's orders to halt.
The rare walk-out is expected to impact hospital care across NSW, with doctors in major Sydney hospitals and regional areas including Tweed Heads and Wollongong voting to strike from next Tuesday.
In a post to social media, the union said the action was needed in response to unsatisfactory pay offers that don't compete with other states.
Excessive workloads, staffing shortages and a lack of engagement in negotiations are also claimed.
"It is likely that the union will face fines in relation to this order," the union said.
"Your council has considered this possibility and is prepared to continue regardless."
It told doctors they will not be personally liable for penalties and directed them to press on in a bid to force further bargaining with the state government.
The union is expected to provide further details of its plans on Wednesday morning.
The Industrial Relations Commission ordered the union to cease organising and refrain from taking any industrial action for three months, a NSW Health spokesman said in a statement.
"If ASMOF members breach the (industrial court's) orders and proceed to action, all local health districts have plans in place to minimise any disruption to patients and hospitals," he said.
The government is also facing a prolonged industrial dispute with the NSW Nurses and Midwives Association which has prompted strikes.
A separate dispute with psychiatrists in the state's public hospitals is due back before the commission on Friday.