Teachers' unions today attacked a plan that would see staff answering email queries from their GCSE pupils outside school hours.
The government is to pilot its "e-mentoring" idea next year as an alternative to traditional study leave, which ministers want abolished.
But teachers' unions said the scheme was "completely unreasonable" and would open the way for pupils to harass staff at home with abusive emails.
Chris Keates, the general secretary of the National Association of Schoolmasters/Union of Women Teachers (NASUWT), called for an urgent meeting with officials to discuss the idea.
She said she was "extremely concerned" by the plan, which seemed to run against government promises to cut teachers' workload.
"It is completely unreasonable to expect teachers to be on-call, online out of hours.
"However, the most serious aspect of this proposal is its potential to leave teachers vulnerable to email harassment and abuse.
"NASUWT will be seeking an urgent meeting with the Department for Education and Skills (DfES) to discuss these issues before the trials on this proposal begin next year."
Steve Sinnott, the general secretary of the National Union of Teachers, said the idea could threaten teachers' privacy.
He said ministers would need to be "very careful" that their liking for new technology did not "blind them to the problems" it could cause.
The schools minister, David Miliband, said on Monday that study leave had become "video-game leave" for too many teenagers and alternatives should be found.
The DfES said one idea that will undergo trials next year will be the "e-mentoring scheme".
"Schools will use the opportunities provided by ICT to support students and answer revision queries by email out of hours," the DfES said.
"School 'clusters' will also be developed where teachers and sixth-formers can support Year 11 students with their revision, particularly out of school hours."
A DfES spokesman added later: "The pilot scheme will be limited to around 15 schools and designed so that it does not add to teacher workloads or expose them to potential email abuses. "We are arranging to meet with NASUWT to reassure them of our intentions and reflect their views in development of the scheme."
He stressed that taking part in the trials would be "entirely voluntary". Teachers should be given time off in lieu or paid overtime for the extra work, he said.