Dinner ladies are being sacked in some schools and their duties carried out by teaching assistants, The TES can reveal.
Collective bargaining is being ignored by head who are negotiating terms and working conditions with individual support staff, their union, Unison, said this week.
Moz Greenshields, of the Derbyshire branch, said schools in her area had carried out sackings. One had sacked four of its six lunchtime supervisors and planned to replace them with teaching assistants.
But David Hart, general secretary of the National Association of Head Teachers, said many heads had to make difficult decisions to stay within budget, and that might mean losing jobs.
"This was never going to be a painless operation because of the requirement to deliver the workforce agreement," he said.
Teaching assistants are seen as vital to the deal, which will give teachers half a day a week away from pupils for planning, preparation and assessment (PPA) time from September.
Ms Greenshields said: "Collective bargaining is being ignored and heads are forcing teaching assistants to sign individual contracts. It is cheap labour cover for teachers or anyone else. Any belief that remodelling offers career development for teaching assistants is not happening in reality."
Unison faces a knife-edge vote at its national conference in Glasgow on Sunday over its involvement in the deal, signed in January 2003. It was intended to bring support staff improved pay and recognition, If delegates back withdrawal, it would leave the agreement operating without the backing of the largest teachers', heads' and support-staff unions.
The Derbyshire branch wants a meeting of the original signatories and the National Union of Teachers, which refused to sign the deal, to be reconvened.
Ms Greenshields said: "We must consider if, with everything that is going on, we are going to remain in the agreement."
Last week, Unison told teaching assistants who are paid just pound;3.50 extra an hour for time spent standing in for teachers to refuse to cover lessons (TES, June 10).
Unison's leaders fear government pledges to consider a national pay structure for school support staff may not be enough to prevent withdrawal from the agreement.
Christina McAnea, head of education, said early discussions on a national structure had begun.
"We want to continue with these talks and that means staying in the agreement for all its flaws, and not being like the NUT and left outside the discussions," she said.