By Angela Harrison
BBC News education correspondent, Liverpool
Teachers work nearly 19 unpaid hours a week, says the NUT
Teachers are threatening strike action in support of a 35-hour week, saying they face an "excessive workload".
The National Union of Teachers, meeting for its annual conference in Liverpool, said politicians had turned a "vocation into a treadmill".
It called for a strategy, including a strike ballot to improve teachers' work-life balance.
The government said that it had already made "massive strides" in cutting teachers' workloads.
This move by the union adds to the pressure on the government which also faces possible strike action over Sats tests in England.
Dealing with 'amateurs'
NUT delegates said teachers worked an average of nearly 19 unpaid hours a week - more than any any other public sector workers.
Patrick Murphy, a teacher from Leeds, told delegates: "For the past 20 years now government policies have turned the job of teaching from a vocation into a treadmill.
"We need to reverse that process."
Sue McMahon, from Calderdale, West Yorkshire, said teachers could not "continue to work in a tick box culture that works against us".
"Our workload has increased, but our professionalism has been eroded by the machinery of government and by Ofsted.
"I am sick and tired of the amateur interference from professional politicians."
Issuing a warning for political parties, she added: "We may end up having a barney with the next government if we as professionals, are not treated as professionals".
The delegates passed the motion on developing a strategy on improving on work-life balance and an amendment to the motion which called for the working week of teachers to be limited to 35 hours.
A charity, which runs a helpline for teachers, says workload is one of the main reasons teachers call.
The Teacher Support Network says of the 16,000 calls it receives a year, most callers complain of stress, anxiety and depression.
The main causes, the group says, are money worries, workload and problems with other adults at work, including bullying.
Chief executive Julian Stanley said: "Workload frequently surfaces as an issue for many of the teachers that use our support line.
"We know many teachers struggle to maintain a healthy work-life balance."
A spokesman for the Department for Children, Schools and Families (DCSF) said: "The government is absolutely committed to reducing workloads ...to free up heads to run their schools and enable teachers to do what they do best - teaching.
"Ministers have made it very clear that it's unacceptable if this is not being implemented."
In 2003 it brought in a workload agreement removing many administrative tasks from teachers and giving them extra planning and preparation time.
Separately members of the NUT, who are head teachers and deputies in England, are being balloted over whether to boycott the Sats tests in maths and English for 11-year-olds.