Giving teachers in FE colleges extra powers to stop and search their students for weapons or electronic devices would "fundamentally change" their relationship, the National Union of Students (NUS) has warned.
Proposals in the Education Bill would give lecturers the right to conduct searches if they believe learners possess items that the member of staff "reasonably suspects" could be used to commit a criminal offence, cause personal injury or damage property.
To tackle online bullying, lecturers would have the power to erase any data or files from electronic devices discovered on students "if the person thinks there is a good reason to do so".
The bill also gives lecturers the power to search a student of the opposite sex even if there is no other member of staff present, if the teacher believes it is not "reasonably practical" to wait for a colleague to arrive.
NUS vice-president for FE Shane Chowen said: "We don't think teachers should be put in a position where they should search students. There's a safety issue, but it also fundamentally changes the relationship between teachers and students.
"This would make the teacher-student relationship more like the relationship between a student and a police officer."
He also criticised the move to tackle online bullying by allowing teachers to search electronic devices.
"This is putting them in the same category as weapons, which seems very odd," Mr Chowen said. "It's a 19th-century solution to a 21st-century problem. Confiscating a phone isn't going to stop cyber-bullying.
"When the senior management team of a college believes there is a need to do something about student safety, they employ professional security staff.
"The security should be at the college gate. We don't want to bring that kind of environment into the classroom. If a teacher believes a student might have a weapon, (they can) call in these people or call in the police."
But the Association of Colleges said FE teachers "need" the option of using the extra powers "as part of a staged approach to behaviour management".
Its submission to the bill committee said: "The extension of the legal powers to search for additional items would . support colleges in their commitment to maintaining a safe learning and working environment for all."
Education secretary Michael Gove said the legislation showed the Government was "absolutely on the side of teachers" and would free staff to "impose the penalties they need to keep order".
Last month, human rights group Liberty described plans to extend schoolteachers' search powers as "proportionate to terrorism investigations".
Ben Bowling, director of criminological studies at King's College London, told The TES that the policy was an "extraordinary extension of powers" that go "beyond those of the police".