He enraged his opponents last week by revealing how executive members had voted on a proposal to give ordinary members more say in policy-making and to allow them to nominate candidates for national office directly. It was the latest round in a battle which looks set to run and run.
The anti-McAvoy faction hit back, accusing their leader of trying to rig the current elections for top NUT positions. They said his decision to release details of voting at the executive meeting, where it was agreed to send a consultative paper and ballot form on greater involvement to the union's 195,000 members, was deeply undemocratic.
They were particularly angry that he had described Ian Murch and Christine Blower, who are standing for treasurer and vice-president, as being on the "extreme Left" of the executive.
Ian Murch is a founder member of the Campaign for a Democratic and Fighting Union (CDFU), one of the two anti-McAvoy groups on the executive.
He said: "The only reason for releasing a statement was because Mr McAvoy wanted to intervene in the election. It is a very bad precedent for the democracy of which Mr McAvoy quite spuriously claims to be the guardian.
"He claims people who are against him are extremists but in the last general secretary election he got only 38,000 votes and his opponent 37,000. If he wants to characterise people as extremists who represent nearly half the union it shows how much he is stretching the term to defend his own position. "
Mr McAvoy has made it clear that he is anxious to clamp down on the increasing domination of activists whose behaviour marred this year's annual conference at which David Blunkett, Labour education and employment spokesman, was heckled and jostled.
He has admitted that his union has been an easy target for far-Left groups and indicated earlier this year that he would take steps towards greater involvement of members in policy-making.
Since Easter he has adopted a new, more pugilistic approach which appears to be paying off. He claimed a significant victory in June when members voted overwhelmingly against a one-day strike over class sizes. The ballot had been called for against Mr McAvoy's wishes at a conference where he suffered a series of defeats. The result, he claimed, proved that ordinary members were not in step with those who dominated the proceedings. His opponents, however, accused him of unduly influencing the result and called for his conduct during the ballot to be investigated.
Conference also decided that the NUT should put in a specific pay claim but members later backed Mr McAvoy's call for a joint submission with the other classroom unions to the School Teachers' Review Body.
"It's increasingly obvious that members are not turning up to local association meetings any more because of their extra workload. The latest consultation exercise is an effort to involve members in determining the union's priorities and actions and to ensure their views are properly represented in the decisions of conference," an NUT spokeswoman said.
"There are 367 NUT associations and divisions which can submit motions to conference but this year only 55 did so, and only 1,171 members out of 195,000 attended those meetings and determined what should be discussed," she added.
If members vote in favour of more involvement the proposals will have to be put to conference. Mr McAvoy is likely to face further stiff opposition.
He denies he has tried to influence the national officer elections and says that the release of voting records has always been at the general secretary's discretion. "I can't tell members how to vote and I wouldn't try to," he says.
But there is no doubt that he is determined to win his battle with the Left. The outcome of the latest election, to be announced soon after November 15 (the closing date for return of ballot papers), will determine just how far he is succeeding.