Sheffield schools face disruption next Wednesday as a result of a proposed one-day national strike by members of the National Union of Teachers.
But fewer classes will be affected than in similar regional stoppages last autumn - as rival union NASUWT has decided against taking part.
The NUT is campaigning against performance related pay, a later retirement age and increased pension contributions.
It is also angry about higher workloads and the number of young teachers quitting the profession.
Primary schools could be worst affected as the NUT is strongly represented in them.
South Yorkshire official Roy Bowser said: “Teacher workload is unsustainable, as a recent Government survey demonstrates - we demand a step-change.
“The thought of doing the job until 68 is preposterous and driving many away from the profession. Teacher morale is at dangerously low levels. Children need teachers who are fresh and well motivated not tired and demoralised.
“We do apologise for the inconvenience to parents but we hope they will support us.”
The NASUWT is holding back on further industrial action until after Easter as Education Secretary Michael Gove has agreed to new talks and has backed down on some issues, such as changes to holidays.