"Don't do it, absolutely not," said Ms Bevan, the NSW Teachers Federation representative at Belair Public School.

"If teaching stayed the way it did and my children went into teaching I'd be deeply concerned and worried for their wellbeing."

Ms Bevan is one of thousands of federation members across the state who will participate on Thursday in historic joint industrial action with the Independent Education Union of Australia NSW/ACT branch, calling for an improvement to non-competitive and unsustainable workloads that the unions say are contributing to staff shortages.

"The teaching profession is in crisis, we are faced with so many different factors but the teacher shortage and the teacher burnout is real," Ms Bevan said.

"When it's impacting schools on the coast in Newcastle you have to think about what's happening with all our colleagues elsewhere in the state out west, how are they dealing with this?

"If I'm splitting my class because I'm at home sick and my kids are constantly going without a teacher, what's going to be the flow on effect?

"Unless something changes our kids are going to suffer."

Federation and IEU members from across the Hunter gathered before school on Wednesday with federation deputy president Henry Rajendra and IEU NSW/ACT deputy secretary Carol Matthews to discuss Thursday's action, when members will gather at Civic Park and march to the state government offices on Bull Street, Cooks Hill.

"We're here this morning to come together as two unions to take on our employer, to call on our employer to deal with a crisis that's plaguing our schools right across NSW," Mr Rajendra said on Wednesday.

"We're in a situation where staffing shortages are impacting on every single school.

"Classes are disrupted, classes are cancelled, we've got merged classes, we've got students left under minimal supervision in libraries, in quadrangles.

"We've got teachers who are burnt out, we've got teachers going above and beyond, we've got teachers covering other people's classes, fundamentally because the government, the employer, has failed to address the staffing shortages."

Ms Matthews said there was already concern about how lockdowns had impacted student engagement with learning.

"It's obvious that having 80 students in a playground being supervised by two teachers is not assisting their teaching and learning, it's not assisting their attachment to school, it's simply making students frustrated and bored and wondering 'What on earth are we doing here?'" she said.

Mr Rajendra said the department's own documents showed there were more than 1900 unfilled vacancies in public schools across the state, an increase of 67 per cent compared to the same time last year.

"We know in terms of the shortages, just in the Newcastle Hunter area and across the regional north area for our public schools, there are over 200 vacancies that remain unfilled by this government, that's just completely unacceptable," he said.

"Yes COVID and the flu have had an impact, but it's only made a bad situation worse again."

He said the problem was poised to "escalate", with student enrolments predicted to grow by 25 per cent over the next 20 years.

Ms Matthews said shortages were being felt across all sectors.

"Catholic schools have estimated by 2030 there will be a shortfall of 4000 teachers, 15 per cent of the workforce," she said.

"This is not a short term problem, this is a long term problem that requires concerted action by the NSW government.

"I think [this strike] is very significant and it's a cry across the profession, right across the profession for something to be fixed, 'let's fix this' and I think that's why it's so historic, is that it is impacting all schools."

Ms Matthews said IEU members were "really demoralised and ground down by the continuing workload", while Mr Rajendra said "the feeling, the resentment the anger that teachers are feeling now completely is outdoing how people felt back in 1996", the last time the unions came together for industrial action.

Teachers are calling for annual wage increases of five to 7.5 per cent, a reduction in paperwork, an increase in preparation time and an end to staff shortages.

The government's new two-year wages policy will give public sector workers a three per cent increase per annum in 2022-23 and 2023-24, with a possible further 0.5 per cent next year for those who contribute to 'productivity enhancing reforms'.

Mr Rajendra said three per cent was "insulting" and "well below the inflation rate".

"Not only are we after salary justice and a competitive salary for all teachers, we're also after addressing significant workload issues on two fronts," Mr Rajendra said.

"Get rid of the 'administrivia', the unnecessary busywork that the employer thinks they need to somehow micromanage our teachers in our schools, but also give them the additional time to sit down with each other, to plan, to collaborate, to make sure we can provide greater one one one attention to our students, because that's what our kids need, that's what our parents are calling for and our teachers know that is the right thing to do."

Ms Bevan, who has been a teacher for 15 years, said many of the colleagues she graduated with have since left the profession, while current colleagues were considering jumping ship.

She said the teacher's aide in her classroom is a trained teacher, who changed roles due to the workload.

"The job is so different [from when I started], the complexity and the intensity of the role - I'm not a teacher," Ms Bevan said.

"What I do is not what I was trained to do, what I did at university is no longer what I do. I'm writing reports and plans and collecting data and analysing data and I'm staying up all night, but I'm not lesson planning and it's exhausting and I'm losing time with my family.

"I'm working 60 to 70 hour weeks to get the job done and at the end of the week all of my paperwork and admin is done but okay, what am I going to teach?"

Ms Bevan said she recently dropped her children at a disco and felt guilty about having dinner with friends instead of catching up on schoolwork. It was 6pm on a Friday.

"It doesn't leave you, you take it everywhere with you," she said.

"There's a preconceived idea we get 12 weeks holidays and it's 9am to 3pm, but it's really not."

She has a USB on her keys. "My kids hear me get the keys out and are like 'Ugh Mum is going to do work'," she said.

"When I first started teaching I used to jump out of bed, I loved it, I loved being in the classroom but the joy is no longer there, it's been sucked right out of it.

"I'm not teaching and when I am my time has been so consumed by doing the admin roles that I'm not the best teacher I can be."

IEU member Paul Dan, who is a teacher at St Francis Xavier's (SFX) College Hamilton, said families understood what was at stake.

"Their children are not getting the education they deserve," he said.

"We as teachers are holding this together and the government is simply not coming to the plate. I know my child is not getting the education his generation deserves and we simply cannot provide that the way things are... we're so tired even our morning coffees need coffee.

"We are working above and beyond and we are getting our entitlements of time - where we can plan and create those really good lessons - they're getting taken away from us, because we're being put on extra duties to cover for the fact that we don't have enough staff there to teach the kids... we want to work with the government but the reality is it doesn't feel like they're even listening to the experts in this instance, which is us."

He said experienced colleagues were leaving and would not be able to mentor new teachers.

"This is the greatest job in the world, but it's being ruined and it's selling out our kids," he said.

IEU member and SFX teacher Michael Sibert, who was an accountant before he joined the profession aged 41, said there was pressure on the government's budget, but education should be a priority.

"Education is a big liberator for all social classes to rise up and have their opportunities realised in an egalitarian society, or a society that likes to think it's egalitarian," he said.

Mr Rajendra rejected the government previously describing industrial action as disruptive.

"Tomorrow's industrial action pales into insignificance when it comes to disruption compared to the uncovered classes, the massive disruptions on a daily basis," he said.

"It's not uncommon - in fact it will happen today most likely - that a large school, say a 500 student school, for 20 odd teachers to be absent.

"That is unacceptable.

"The strike is a demonstration of strength to highlight that the government has failed our schools right across NSW. Failed our schools.

"What greater responsibility do they have than providing the essential public services our communities deserve and need, particularly when it comes to education? They've failed and we'll be sending a very very strong message tomorrow."