Kotara High's Sean Brown has been teaching around the Hunter for almost 30 years. He said unless government takes action to address unsustainable teaching workloads and uncompetitive salaries, NSW will face a "massive" teacher shortage in the next decade.

"The region already has teachers outside their subject area which has a real effect on student outcomes," Mr Brown said.

"It also means students are being left with minimal or no supervision at times.

According to Mr Brown, who is also president of Newcastle teachers Association, increased administrative burdens are diminishing teachers' ability to focus on education and adding to already high workloads.

He said an ageing casual workforce won't be able to meet the requirements of a growing student population without more students graduating university.

"The only way we are going to attract more teachers to the professional is through increased salaries and decreased workloads."

Prepare to strike:

Teachers Federation senior vice president Amber Flohm was in Newcastle on Tuesday to "support teachers in the Hunter area" ahead of Wednesday's strike.

As the Newcastle Herald reported last Wednesday, the Teachers Federation are calling for a pay rise of between five and 7.5 per cent per year, plus two extra hours of planning time per week.

The government's public sector wages policy caps pay rises at 2.5 per cent per year.

Ms Flohm said there are currently 114 permanent vacancies across public schools in the Hunter and that the industrial action is to "address the fundamental causes of the teacher shortage".

"The teacher shortage is biting everyday in our schools and that's the disruption that we are facing," Ms Flohm told media out the front of Merewether High.

"If we do not pay teachers a competitive salary and address the crippling workload, we will fail to attract the new teachers that we need and retain the ones we have."

Calling out the "failure of this government to take action" Ms Flohm dismissed Education Minister Sarah Mitchell's announcement this morning to delay wage negotiations before the Industrial Relations Commission until after the June 21 budget as "tinkering around the edges".

"It does absolutely nothing to address the fundamental issues for our professions," she said.

"We are yet to meet a parent in NSW who wants their child taught maths or science by an English teacher.

"You may be a qualified tradesperson but a plumber doesn't equal a carpenter, doesn't equal an electrician."

'Disappointed' government calls for no strike:

A spokesperson from the NSW Department of Education said the department is "deeply disappointed" in the union's decision to strike and said action from teachers will be deemed "unauthorised absence" with staff going unpaid.

"We call on the Federation to put students first and call off the planned industrial action," the spokesperson said.

"Parents want their children in school, and no student needs another day out of the classroom."

Schools must remain open for students on Wednesday, with principals advising parents and caregivers of specific arrangements, the spokesperson said.

"They will advise parents and caregivers of the arrangements for their school," the spokesperson said.

"In some cases schools will provide minimal supervision, which means temporary class structures and a modified timetable are needed to meet safety and supervision requirements."

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