The National Union of Teachers is at loggerheads with ministers over their alleged continuing reluctance to set in law the tasks that only teachers can do.
It warns that the stance leaves the Government open to accusations that it wants to allow lowly-paid support staff to take on teaching roles.
The claims came as a Department for Education and Skills policy statement listed 45 tasks, from setting up classroom displays to taking the register, that teachers could hand over to support staff.
But the statement, circulated to peers during the Education Bill's passage through the House of Lords last month, said the Government had no plans to set out in formal regulations or guidance the tasks that only qualified teaching staff should perform.
John Bangs, head of education at the NUT, said: "The Government is walking on eggshells at the moment on this issue. Teachers worry that ministers have an agenda of putting unqualified staff into teachers' jobs.
"I'm not sure that is their intention, but they risk being accused of that unless they take the chance to clarify the situation."
Teachers and union leaders have voiced concerns about lower-paid support staff being employed effectively as teachers since Education Secretary Estelle Morris revealed plans last November to change the law to allow classroom assistants to take lessons in some circumstances.
The issue has been a point of dispute during long-running talks on how to cut teachers' workloads, which will draw towards a conclusion next month when the Government publishes its proposals for tackling the problem.