Head of education John Bangs has claimed his two rivals for the post of National Union of Teachers' general secretary are compromised by the support they get from organised political factions within the union.
In a letter asking NUT local associations for nominations, in which he describes himself as the only independent candidate, Mr Bangs writes that his opponents' campaigns will be "led, organised and financed by those who support such factions.
"Were either to be elected, their decisions and advice would be fettered by those factions."
Steve Sinnott, the deputy general secretary, has responded with his own letter which refutes the claims and implies that Mr Bangs, the NUT's head of education, has been involved in negative campaigning and allowing the contest to "sink into sniping factionalism".
Mr Bangs told associations that he believed the approach of John Illingworth, who has the backing of the left-wing Socialist Teachers Alliance and the Campaign for a Democratic and Fighting Union, would be to "embrace industrial action as an end in itself, as the first solution and not the last".
Mr Illingworth, a former NUT president and Nottingham-based headteacher, said the claim was "crazy".
He said it was naive to think that any candidate was completely independent of organisations within the union. But if elected as general secretary, he would represent the union as a whole and not allow any faction to determine what he did.
Mr Bangs, the preferred candidate of Doug McAvoy, the current general secretary, also used his letter to suggest that Mr Sinnott would abandon the NUT's policy of opposing the workload agreement because it allowed unqualified staff to teach.
Mr Sinnott said Mr Bangs had taken a quote from his election address out of context and "filleted" his words to make them appear as though he were saying something different. He said he had already made it clear that he thought only qualified teachers should teach children.
"It is a ludicrous accusation," said Mr Sinnott. "I find it really, really regrettable and I hope it doesn't happen again."
He said that while he had the backing of the moderate Broadly Speaking faction, he had not been a member of any group within the union since taking up his post in 1994, and was not being financed by any faction.
The respective letters are published on the candidates' websites. For more details see: www.stevesinnott.org.uk