A row between England's two biggest teaching unions over the use of classroom assistants has deepened.
The NASUWT supports the "historic" workload agreement
The National Union of Teachers - which opposes allowing classroom assistants to take charge of classes - stoked up the row with the other big union, the NASUWT, by accusing it of giving up the right to free speech when it signed up to the workload agreement.
NUT General Secretary Doug McAvoy told delegates at their annual conference in Harrogate that the NASUWT had signed up to promoting the government's agenda.
The Labour government, he said was behaving in a "sinister, totalitarian" regime.
"It's deeply worrying that in a democratic society a government should require free trade unions to commit themselves to its agenda, " he said.
That angered Eamonn O'Kane, general secretary of the teachers' union the NASUWT, who said it was ridiculous to suggest unions which supported the new deal were giving up their right to free speech.
"It's an insult to the NASUWT and the other unions which have signed the deal," he said.
"The agreement does not mean any surrender of principle. It will result in a substantial reduction in workload and that should be the aim of any trade union."
While the NASUWT says there could be industrial action if schools say they cannot afford the changes being brought in - the NUT is threatening disruption if the changes are brought in.
On Monday, the NUT conference heard calls to stop classroom assistants taking charge of classes - including the unilateral imposition of class size limits which could see pupils being sent home.
The NUT says that using classroom assistants in such an independent role will undermine the professional status of teachers.
Under the new workload deal, school teachers will be allowed time out of the classroom to prepare lessons and for marking.
Classroom assistants will take on administrative work and "higher level" assistants will be able to supervise classes unaccompanied.
Before the NASUWT's annual conference in Bournemouth, Mr O'Kane said he was concerned some schools might say that budget shortages would delay the new working practices.
Some schools are warning they might have to cut school staff because of funding problems.
But Mr O'Kane said the reforms represented the fruits of years of lobbying and in recent years, detailed negotiations with the government.
They would improve teachers' working lives greatly and should be defended, he said.
"If any attempt is made to frustrate the implementation of the deal, we would react strongly - with industrial action if necessary," he said.
Meanwhile, on Tuesday the NUT's conference will vote on how its members might oppose the use of classroom assistants to take charge of lessons.
The use of assistants will be debated at the conference in Bournemouth, with the NASUWT's executive calling on delegates to support the workload deal.
There will also be discussion about testing and exams. It is thought a motion might be put forward calling on teachers to boycott national tests which children take at seven, 11 and 14.
Union leaders will ask delegates to reject that call on the grounds that the boycott would be illegal.
Also be debated at the NASUWT conference will be the future of A-levels and GCSEs, and the problem of the racial harassment of teachers.