Teachers are to be balloted for potential strike action in support of a colleague who was sacked for wearing trainers and tracksuit bottoms.
Adrian Swain was fired from St Paul's Way Community School in Tower Hamlets, east London, after he refused to follow instructions from his headteacher to wear more professional clothes.
Mr Swain, who had been at St Paul's for 17 years and a teacher for 35, said there needed to be proper consultation before a dress code was imposed. He had worn similar clothes throughout his career without complaint, he added.
Members of the NUT are now expected to take part in an indicative ballot for industrial action within the next week. If there is support, an official ballot is expected to follow.
Unison, the union that represents support staff, said it was also appealing against the sacking of a student welfare officer at the school, and would urge members not to cross a picket line.
Mr Swain, who was his school's NUT rep, said he had lost his job because of heavy-handed management and the "arbitrary decision" of the head, Lorraine Page, to impose new rules. Ms Page left the school at Christmas.
"There was no consultation with staff. We were just told the rules were changing," he said. "I was told I was not a good role model for students. No one has ever accused me of that before in all my years in the classroom.
"The dress code has been used as a bully's charter and I could not go along with it. Professional dress could mean nothing or everything, depending on the head's whim."
Mr Swain, a maths teacher who had recently taken up a post in the school's unit for deaf pupils, said he would file an official appeal against his dismissal this month.
He was sacked at the end of the autumn term for failing to comply with a "reasonable management instruction". The head introduced the rule on trainers at the start of the school year, Mr Swain said.
A spokesman for Tower Hamlets council said it was important that standards of appearance were set by staff, and they should not wear clothes that pupils were not allowed to wear.
The student welfare officer was sacked after failing to do enough to help a pupil who had been injured when falling off a chair in class. The officer was on her unpaid lunch break when the incident occurred, so sent the pupil to the main school reception. The child's injuries required an ambulance to be called.
Jean Lane, Unison's assistant secretary for education in Tower Hamlets, said that in other schools the staff member would probably have received a warning, not been fired. "We are convinced that the management wanted to frighten people," she said.
Ms Lane praised the stand taken by Mr Swain. "It's hard, in this climate, to put your job on the line for a principle," she said.
Mr Swain's case will be referred to the General Teaching Council for England. A spokeswoman said the case would be looked at by officials, who would decide whether any further action was necessary.