For the first time in 25 years, public and Catholic school teachers will strike together in demand for better pay in New South Wales.
Ongoing negotiations with the state government have led to a pay increase offer of three per cent.
But teachers have rejected the offer, calling for a bump of between five and 7.5 per cent.
They say they are overworked and underpaid.
"I can assure you that the last thing that teachers want to be doing is to be taking to the streets," NSW Teachers Federation president Angelo Gavrielatos said.
"I can assure you that teachers and principals would prefer to be doing is taking care of the students much."
Teachers will rally at Hyde Park before marching on State Parliament.
Up to one million students are expected to be affected by the strike action.
Meanwhile, commuters are expected to be faced with another day of chaotic travel in Sydney despite the government agreeing to the rail union's terms.
Transport Minister David Elliott said yesterday the government would spend more than $260 million to address safety concerns from train drivers about the new fleet.
However, the union says they want the offer in writing, which they will take to their members for a vote.
It's hoped that will happen in the next 24 hours, preventing the industrial action from continuing tomorrow.
However, as of today, it's going ahead, meaning rail services in the city will be cut by up to 70 per cent.