Teachers have voted to boycott a pupil who added an "offensive" caption to a photo of a female colleague.
Teachers are concerned about the use of camera phones
The boy was caught by another member of staff at St Cuthbert's RC school in Newcastle upon Tyne.
Members of the NASUWT and ATL unions voted to refuse to teach the boy, who was expelled but later reinstated when his parents won an appeal.
The school said that, in view of the ballots, it was trying to make other arrangement's for the boy's education.
ATL general secretary Mary Bousted said: "At the ATL's recent annual conference our members voted unanimously to urge the government to provide teachers with supportive guidance and clear rules on the issue of mobile phones in schools.
"The situation at St Cuthbert's school clearly highlights how the exploitation of advances in mobile technology are threatening teachers and other educational professionals who should be protected."
The NASUWT, which has 32 members of staff at the school, balloted its members before Easter - its boycott starts on Wednesday.
Its deputy general secretary, Jerry Bartlett, said the photograph was taken without the teacher's knowledge - constituting sexual harassment in the view of the NASUWT.
Mr Bartlett said: "Our members will not teach the child concerned because they consider that he constitutes a hazard to the health, welfare and safety of the teachers in the school."
He attacked the decision by the independent appeal panel to overturn the boy's exclusion from the school as being "irresponsible".
The school's head teacher, Gerard Murphy, said it was the caption added to the photo that the teacher, the school and governing body had found offensive.
"Because of the nature of mobile phone technology there is a possibility that the photograph could have been circulated to other pupils but I have found no evidence that this actually occurred," he said.
St Cuthbert's acknowledged the outcome of the ballots and was striving to make the best possible arrangements for the pupil's education in the circumstances.
The NASUWT's national executive member for north-east England, Mick Lyons, added: "I can't see any reason whatsoever why pupils should have camera phones in schools."
The NUT is also balloting members on the matter.
Taking a stand
In its most recent Ofsted inspection report St Cuthbert's, whose former pupils include pop star Sting and football coach Laurie McMenemy, is described as a very good school with some outstanding features.
The ATL's regional officer for Newcastle, Ray Butler, added: "This incident highlights the increasing concern teachers have regarding their right to privacy.
"ATL members have taken a stand by refusing to teach this pupil, and their action will hopefully prevent other staff in schools being bullied in this way."
The Department for Education and Skills said all schools should have clear policies in place on the possession and use of mobile phones with clear sanctions to deal firmly with their misuse.