Schools are using CCTV cameras designed to keep pupils safe to spy on teachers, it has been claimed.
Teachers are being subjected to "permanent surveillance", with school leaders monitoring the footage and using it to make judgments about the performance of their staff, according to the NASUWT teaching union.
In many cases, teachers say they cannot turn off the cameras in their classroom, which are constantly recording lessons, a poll conducted by the union found.
The survey comes as delegates attending the NASUWT's annual conference in Birmingham debate a resolution warning that monitoring of teachers is becoming excessive.
It says that this monitoring goes beyond any reasonable justification, or value to pupils' progress.
The motion adds: "Its impact is to stifle creativity in education, disempower teachers, put procedure before purpose and increase the workload of teachers."
The NASUWT's survey found that of the 7,500 members questioned, around one in 12 (8%) said that they have CCTV in their classrooms.
Of these, two thirds (66%) say the cameras were introduced for pupil safety, with a further 58% saying they were brought in for the safety of staff.
Just under a third (31%) said that the cameras are there to monitor pupil behaviour, with 15% saying that they are designed to help teachers' professional development.
About 7% said that their school had introduced cameras to monitor teaching and learning, with another 6% claiming they are used to monitor teacher performance.
One teacher said that in their school: "CCTV has been used against staff to imply they are handling a situation incorrectly even though the CCTV has no sound."
Another said: "In my school it has been used specifically with newly qualified teachers (NQTs) that the senior leadership team think are not performing well."
Almost nine in ten (89%) said that they cannot switch the cameras off, with a similar proportion (87%) saying that the CCTV was constantly recording.
The survey also found that just over half of teachers (55%) claim the recordings are monitored by their school leaders, with two fifths (41%) saying the footage has been used to make judgments about staff.
Around 17% of those questioned said that they see the CCTV as there just to spy on teachers, with 31% arguing it is an invasion of their professional privacy.
NASUWT general secretary Chris Keates said: "Teachers are already wrestling with excessive monitoring, masquerading as classroom observation, carried out by senior management and a host of other people regularly visiting their classrooms.
"Now, in some schools, they are being subjected to permanent surveillance through CCTV cameras. Lab rats have more professional privacy."
She added: "The stories teachers recounted to us in the survey are a shocking catalogue of professional disrespect and unacceptable intrusion.
"No other professionals are subjected to such appalling treatment, No one should be subjected to the stress and pressure of being watched constantly."
:: The NASUWT questioned about 7,500 teachers between February 21 and March 10.