At least 60 schools (lycees d'enseignement professionel) in the Ile-de-France region around Paris, and others in cities including Lyon, Dijon and Nantes, have been on strike since the start of the month.
Demonstrations have been held against a new schools' charter, adopted last week, which protesters fear will damage their conditions of work and quality of teaching. But education minister Claude Allegre said he wanted to raise the status of the teachers working in what is often regarded as the poor relation of upper secondary education.
He recognised that vocational secondary teachers had a wide range of skills and worked longer hours than colleagues in general or technological lycees.
Mr Allegre wants to reduce the time worked - both by the 708,000 vocational pupils who clock up to 45 hours a week, and by teachers whose statutory weekly timetabl he plans to cut from an average 23 hours of classroom teaching to 18, in line with teachers in other lycees.
He also aims to raise the cachet of the schools and make their training more relevant to the needs of business and the economy by building a closer partnership, with official training contracts, between the schools, pupils and the companies which offer workplace training.
Participating firms should be entitled to use the lycees' technological facilities in return for training and hiring the pupils, he said.
But while the principal union representing LEP teachers supports the reform, five others have mobilised members against the measures, which they claim will reduce pupils' training time - though they will have to follow the same coursework - and put an end to teaching in small groups.
They also fear some teachers may "owe" teaching time, since their working hours are based on a notional calculation dependent on the numbers of pupils and skills being taught.