Eight out of 10 teachers have considered leaving the profession because of their heavy workloads, it has been claimed.
Long hours on "unnecessary" work is demoralising school staff and leading to a "crisis" in teacher recruitment and retention that could damage children's education, according to the NUT section of the National Education Union (NEU).
In some cases, work pressure is leaving teachers exhausted, and even putting marriages under strain, it was suggested.
Ministers have pledged to cut teachers' workload.
An NEU survey of more than 8,000 of its members found that 81% say they have considered leaving teaching in the last year because of the pressures of workload.
40% of those polled said they spend more than 21 hours a week working at home during evenings and weekends.
One teacher told the union: "I don't know how I can change how I work, I don't know how long I can maintain it, and the impact that it's having on my family is horrific.
"I am near marriage breakdown and one of the reasons is my job."
Another said: "We are not trusted to get on and do our job. We are accountable at every level, which creates more stress and paperwork.
"We are exhausted, and great teachers are being driven out of the profession because they are burned out!"
NEU joint general secretary Kevin Courtney said: "The continual long hours spent on unnecessary work such as data collection for arbitrary Government targets is not only demoralising but is unsustainable mentally and physically.
"If the Government does not act decisively and soon, the recruitment and retention crisis will seriously damage our children and young people's education."
Ministers have announced measures aimed at cutting teacher workload.
Earlier this month, Education Secretary Damian Hinds pledged to cut teachers' hours and workload in a bid to tackle staff shortages in schools.
In his first major speech, he promised school leaders that the Government would "strip away" pointless tasks to allow teachers to "focus on what actually matters".