Victorian high school teacher Euan Morton has just come off a daunting holiday period swamped by practise exams from his Year 12 students.
"You've got every student, multiplied by three essays per exam, if you do a couple of exams, all of a sudden during your holidays you've got 200 essays to mark," he tells AAP.
It's an example of the "unsustainable" workloads thousands of teachers have to endure, the Australian Education Union says.
It is preparing a protected action ballot to go to the Fair Work Commission for authorised industrial action.
While Mr Morton doesn't want to strike and potentially miss class time, he admits the problem must be addressed.
He says on average he does about 14 hours overtime a week, working past midnight on many nights to keep up.
The union says it's the student's that ultimately suffer.
"Over two-thirds of teachers don't have enough time to plan their classes to the level that they would want," AEU Victorian Branch president Meredith Peace said.
"The whole system is at breaking point."
The current enterprise bargaining agreement expired in October and staff have not had a pay rise since 2015.
AEU negotiators are expected to meet with Education Department officials in coming weeks to discuss a new EBA.
Minister for Education James Merlino said on Saturday "our teachers do an amazing job and we will continue to bargain in good faith over their EBA".
