Industrial action by teachers in a row over jobs, pay, pensions and workload is to start a week later than planned to avoid a possible legal challenge to the wording of notices sent to employers.
Members of the National Union of Teachers (NUT) were due to start a campaign of action short of a strike from Wednesday, but it will now be launched on October 3.
The union is taking action with members of the NASUWT, who are already involved in an industrial campaign.
Christine Blower, general secretary of the NUT, said: "While there has been no official court challenge to the notices given out to employers, there has been an indication of a possible challenge to the wording of the notices.
"Legal advice suggested that the notices were in fact sound. However, the NUT has taken the decision that rather than get embroiled in a pointless legal row which could potentially detract from the real issues we would simply reissue the notices.
"The NASUWT and the NUT are campaigning together to defend teachers and protect education. The united approach of the two unions, representing nine out of 10 teachers, provides an opportunity to put pressure on the Government to address the continual attacks on the teaching profession.
"The action we are taking at this stage will have a positive benefit on children's education and restore a balance to the working lives of teachers.
"The continual attacks on the teaching profession and the erosion of working conditions and pay cannot go on."
The action involves teachers across England and Wales.
The NASUWT, which has been involved in action short of a strike since last December, confirmed the escalation of its industrial action will take place as planned from Wednesday.