The conference heard how excessive workload and working hours are adversely affecting the health and wellbeing of teachers, contributing to the growing crisis in recruitment and retention, and ultimately affecting standards.
Addressing delegates at Cardiff's Millennium Centre, executive member Keith Muncey, said: "Complaining does nothing. We have to get to a point where we do something about it. We condemn excess working hours. If you ask any teacher how work is going the answer will be the same. A recent survey found that 80 per cent of teachers said workload was the number one issue."
Chris Keates, general secretary of the NASUWT, said: "Teachers are exhausted and their health and wellbeing is deteriorating.
"Teachers are being betrayed by ministers and employers, who are well aware of the problems and do nothing to address them."
She said annual research conducted by the NASUWT showed that year-on-year since 2011 workload and working hours have been rising, adding: "Excessive workload is driving talented teachers out of the profession, deterring new entrants and damaging the health and wellbeing of those who remain."
Delegates unanimously passed a motion to support the union in its continuing industrial action campaign to secure changes to policies and practices which drive excessive workload and working hours.
The motion also called for a limit on working hours to protect teachers against exploitation.
Seconding the motion, Richard Kempa said: "Teachers are being exploited."
He cited the example of one teacher who calculated his working hours per week at an average of 59. When asked for the number of hours his employer was expecting him to work he calculated that at 74. Mr Kempa added: "He is working 59 hours, but he feels like he is failing."
He cited a recent wellbeing survey which found that 91 per cent of teachers said they had considered leaving the profession.
Examples were given of teachers who missed out on time with their family because work got in the way.
Summing up, Mr Muncey said teachers should be empowered to say no and to work with their union reps to make a change.
"What I can't understand is why teachers continue to work these ridiculous hours. Work is a means to an end. For the majority of our colleagues it is the end, it is all they do. We will defend against ridiculous exploitation of teachers."