NASUWT General secretary Chris Keates said unions were trying to keep the action "pupil and parent friendly", such as cutting down on paperwork.
But she warned the position could change, especially after a report from the teachers' pay review body later this month.
A teacher with six years experience has lost £5,500 through a pay freeze and pension changes, while those in the job for two years had lost £3,500, she said:
Teacher morale is at an all-time low and our research shows that over half are seriously considering leaving the profession.
More top news
A British amateur sailor died this morning after being hit by a sail while taking part in the Clipper Round The World Yacht Race.
Plans for seven-day GP services are "unrealistic" because of a shortage of doctors, the Government has been warned.
Forty-one people have been injured, four seriously, after a Welsh tourist coach was involved in a pile-up on a Swiss motorway.