The Government's deal with the unions on workload came under attack this week from the traditionally moderate members of the Association of Teachers and Lecturers, who threatened industrial action if it failed to improve working conditions.
It was the first stirrings of grassroots' concern over the deal signed by the leaders of eight unions, ministers and employers.
In Blackpool, this week, delegates of the union with 160,000 members, expressed fears over the threat to teachers' professional status posed by the agreement, which enables support staff to take lessons and questioned whether schools would have sufficient funding to make the changes.
David Miliband, schools minister, tried to reassure them by saying that half a billion pounds was still with local education authorities waiting to be allocated to schools.
The minister was greeted with cries of "shame" when he later tried to press home his point to delegates during a hostile question and answer session.
Earlier, members had agreed to back the workload agreement, but said they would want to withdraw if there was insufficient funding.
The union then, unexpectedly, went further by voting for a reserve option of balloting for industrial action if the agreement "detrimentally affected" their workload and conditions of service.
Jean Webster, from Porthleven community school, Cornwall, said: "This may be a good deal for ambitious teaching assistants. It is certainly not a good deal for classroom teachers. Most importantly it isa lousy deal for the nation's children."
Helen Brook, from Morley Memorial primary, Cambridge, said: "If the price of limiting workload is to end a graduate-based teaching profession then it is not worth the paper it is written on."
Delegates had earlier unanimously passed an emergency resolution calling for the Government to produce evidence that money provided for the workload agreement was not used to avoid redundancies caused by the schools' funding crisis.
Mr Miliband told delegates that 70 local education authorities had shown they had more than pound;250 million of funding destined for education between them. Some were holding on to more than pound;10m. He said this indicated there was still another pound;500m in the system for English schools.
Graham Lane, education chair of the Local Government Association, said:
"Certainly no authority has held back money from schools deliberately."
Mary Bousted, the ATL's new general secretary elect, was due to use her maiden conference speech today to tell delegates that teacher retention should be at the heart of every government education policy.
"Everybody would have sympathy with the Goverment's desire to raise educational standards. But what we have to question is the strategies which they use which all too often take away from professional autonomy," she said.
She was expected to back members concerns that the professional status of teachers must be protected through a clear demarcation between their role and that of the higher-level teaching assistants.
The ATL's no-canvassing rule for general secretary candidates meant that the conference was the first time Dr Bousted had been able to meet members since being elected to the post. She will replace Peter Smith who is due to retire in July.
Conference delegates voted overwhelmingly to abandon the rule on Monday.