Teachers at Pope John Paul II secondary school, Salford, are taking strike action next week over proposals to increase the school day. The management had intended to start the school day 15 minutes earlier.
Peter McGloughlin, regional officer for the National Association of Schoolmasters Union of Women Teachers, said: "My members have expressed strident opposition to the plans and we are particularly concerned about the lack of consultation."
The union is also likely to ballot at Moorside High School, Salford, over proposals to alter lunchtime and other teachers' breaks.
Chris Keates, NASUWT regional officer in Birmingham, has seen an increase in the number of school managements attempting to lengthen their hours. So far the union has managed to reach a compromise with governors in cases where the staff has disputed the proposed changes, but Ms Keates is worried about the trend.
She said: "My worry is that the decisions do not seem to be based on sound educational grounds. The pressure of Office for Standards in Education inspections are prompting managements to do things that look good on paper. But we have no evidence that making the school day longer is an improvement.
"In some cases the governors suggest say an extra 10 minutes a day. That does not sound unreasonable until you work out that it means an extra three days a year without extra pay.
"We are also suspicious about the motive for shortening and staggering teachers' lunch breaks. It seems to be more about saving money on lunchtime supervisors than delivering the national curriculum."
Hilary Pollard, a Association of Teachers and Lecturers branch secretary in Kirklees, said schools' decisions to change hours have caused a great deal of unrest. Staff at her school, Rawthorpe High, have agreed to shorter periods.
"This will mean we will have at least one extra class a week to teach, " she said. "We have agreed to try out this arrangement, but if it results in a greater workload we will be arguing to end the experiment."
Dave Burgen, head of Herries school, Sheffield, fears problems this term. His governors have increased the teaching hours from 22.5 to 25 hours in response to an Office for Standards in Education report by eliminating the afternoon break and starting 10 minutes earlier. "The staff aren't very happy about it," he said.
Lack of consultation is a major concern of union officers. Teachers at one school found out that their breaks were to be shortened from a notice on a Friday to take effect from the Monday.
The length of the school day is not determined by statute. It is the responsibility of the governing body to decide the length of the school week. Yet, according to a DFEE circular, many schools are not spending sufficient time on lessons.
Eamonn O'Kane, deputy general secretary of the NASUWT, said: "We will support any members who feel their workload is being increased or their conditions of service worsened."