Unions say the NSW government's "war on wages" has escalated, as the premier says unions involved in illegal strikes should face the "hardest fines possible".
The government plans to impose maximum fines of up to $55,000 for the first day of illegal industrial action and $27,500 for each subsequent day.
The penalties will also see unions fined $110,000 for the first day of an illegal strike, and $55,000 on each following day.
"It's very clear when the Industrial Relations Commission finds a strike to be illegal ... there should be the requisite penalties in place," Premier Dominic Perrottet told reporters on Thursday.
"These are strikes the Industrial Relations Commission has deemed to be illegal," Mr Perrottet said, referencing industrial action by NSW Paramedics in March, and a health workers' strike in April.
"If the union bosses conduct illegal strikes, inconvenience families right across NSW, then they should be hit with the hardest fines possible.
"And that's what this change today will do."
Mr Perrottet said the increased penalties were in line with every other Australian jurisdiction.
Secretary of the Australian Paramedics Association Alan O'Riordan sad the move was a "disgrace".
"Having turned its back on frontline workers, the government now wants to intimidate us into silence," Mr O'Riordan said.
"It's unconscionable that the government would seek to punish working people rather than meaningfully engage with what those on the frontline are saying our state needs."
He said action was being taken by nurses, paramedics and teachers to benefit patients and students.
"Workers are voting for industrial action because their government is refusing to listen."
Nurses and teachers are planning to walk off next Tuesday and Thursday respectively, in response to the government's budget this week.
They are unhappy with the three per cent public sector pay increase, saying it is a cut to real wages and does not address crippling workloads and staff shortages.
"My understanding is that the unions will continue to take action," Unions NSW secretary Mark Morey told 2GB on Thursday.
"If you've got teachers and nurses on the street there's something fundamentally wrong with the system.
"They are on the street because they are losing staff, they're underpaid and overworked."
The government has flagged it will introduce amendments to the Industrial Relations Act to impose the bigger penalties.
Employee Relations Minister Damien Tudehope said the fine hike would deter unions from disrupting essential services.
"Illegal strike action has had incredibly damaging consequences for students, families and workers across the state," he said.
Last month's strike by teachers shut down more than 450 public schools, affecting more than 700,000 students.
Current penalties allow for a $10,000 fine for the first day of an illegal strike and $5000 a day after that. If an organisation has previously been penalised, there is a maximum of $20,000 for the first day and $10,000 a day thereafter.
