NSW Premier Dominic Perrottet says he's disappointed after public school teachers called a statewide strike.
Teachers are unhappy over what they say is the government's failure to address unsustainable workloads and uncompetitive salaries.
Joined by principals, they will walk off the job for 24 hours on Tuesday December 7.
Teachers Federation president Angelo Gavrielatos says he and his council voted unanimously for the stoppage in Sydney on Saturday morning.
"This will be the first 24 hour stoppage in a decade and it reflects the gravity of the situation we find ourselves in," Mr Gavrielatos said.
A statewide advertising campaign will also be stepped up with TV, radio and print advertisements focused on the failure of the government to fix teacher shortages.
"The Perrottet government is refusing to listen to the warnings of its own education department that the unsustainable workloads and uncompetitive salaries of teachers are contributing to growing shortages and turning people off teaching," Mr Gavrielatos said.
"This is about the future of the teaching profession and the quality of education children receive.
"No student should miss out because of a lack of teachers but this is what is going to increasingly happen across NSW if the government fails to act."
Mr Perrottet told reporters on Saturday the news was disappointing.
A 2.5 per cent pay rise - the government's offer from day one - is "fair and reasonable" in circumstances where hundreds of thousands of people across the state have lost their jobs, he said.
"Having said that, we want to make sure we do everything we can to provide the best support for our teachers, who are doing a fantastic job right across our state.
"(When) we can provide more support we will," he said.
The premier said he'd had "incredibly constructive" discussions with Mr Gavrielatos over the last few days, including on Friday, and would continue to work closely with them in addressing the workforce's concerns.
Mr Gavrielatos said teachers and principals had, over the course of the past 18 months, exhausted all options to arrive at a negotiated settlement.
He said the government had also declined to increase teachers' planning and preparation time outside the classroom, which for secondary staff, has remained unchanged since the 1950s.
The NSW industrial award that determines the salaries and conditions of teachers expires in December.
Mr Perrottet said the pay issue would ultimately be resolved at the Industrial Relations Commission.
Reports suggest all 2200 of the state's public schools could be impacted by the industrial action, with as many as 60,000 teachers considering taking part.
Australian Associated Press