Teachers at Margaret Thatcher's old school this week became the latest to decide to strike over changes to senior staff pay, which could cost individual teachers up to pound;10,500 per year.
Forty members of the second-largest teachers' union, the NASUWT, at Kesteven and Grantham girls' school in Lincolnshire, were due to strike yesterday after failing to agree a compromise over proposals which would cut the salaries of up to 12 teachers.
Chris Keates, the NASUWT's general secretary, accused the school of trying to intimidate teachers into accepting salary cuts by threatening to deduct pay from those working to rule.
Lynda Poole, the school's headteacher, said she had carried out its review of staffing in line with government guidelines.
The NASUWT had offered to suspend action at Kesteven and Grantham for 21 days if the school agreed to constructive talks.