Last week, heads in Nottingham and Salford held meetings to voice concerns about the final phase of the workforce agreement which guarantees teachers 10 per cent planning, preparation and assessment (PPA) time from September.
Like the Essex heads who met last month, they fear standards will fall unless they are given enough funding to use qualified teachers as cover during PPA time.
In Salford, 52 of the city's 85 primary heads - members of both the National Association of Head Teachers and the National Union of Teachers - met and there were letters of support from another 20. They are writing to parents and local MPs saying that teaching assistants have been trained for a maximum of 50 days and using them to take whole classes would "lead to a dilution of the teaching profession and a lowering of standards".
Francis Hartley, head of the Deans primary, said: "The Government is very hot on principles and rhetoric but low on practicalities."
In Nottingham, around 60 of the city's 95 primaries heads met, with letters from another 10. John Illingworth, head of Bentick primary, said: "We are not going to give up all our hard work in raising standards just because someone has come along with the outrageous suggestion that anyone can teach."