Eamonn O'Kane, general secretary designate of the National Association of Schoolmasters Union of Women Teachers, wants the association to consider a merger with the other two largest unions to create a super union of 500,000 members.
Last month, The TES reported that he was circulating a paper to members putting forward the idea of unity with the National Union of Teachers and the Association of Teachers and Lecturers.
But the paper is now likely to be circulated alongside counter-arguments setting out how the NASUWT might thrive without a merger. Fellow national executive members said that rival views needed to be put to the NASUWT's 200,000 members.
Mr O'Kane originally wanted the paper to go directly to this year's annual conference. A recommendation to that effect was put to the union's executive last month but rejected. There were concerns among executive members this week that the paper could have been rushed through without proper discussion.
One said: "There is a hard core of us dead-set against this and a hard core in favour of it, and a lot of people sitting on the fence."
Another said: "Executive members were unhappy with the speed with which it was going forward, and wanted to look at alternatives. The general view of the executive was 'let's go slowly on this'."
One suggestion within the NASUWT is that Mr O'Kane could end up as general secretary of the proposed new body, with current deputy NASUWT general secretary Chris Keates as his deputy. However, many members are sceptical.
Doug McAvoy, NUT general secretary, is due to retire in 2004 and Peter Smith, the ATL general secretary, goes in 2005.
Mr O'Kane, who is also due to retire in 2006, said that he was "relaxed" about alternative views being put to members. He said: "I have always accepted that there would be countervailing arguments which have a different perspective and set out a different conclusion.
"It's clearly a very important issue, and one where there are different views very strongly held. Why wouldn't there be? After all, the traditional view of the NASUWT has been not to go down this route.
"At the end of the day, people are going to have to make up their minds. I want to make sure it gets a full debate in the union."
He said it was nonsense that people were talking about him being leader of the super union. "I am sorry that people think in those terms."
The NASUWT has traditionally been the most opposed to a merger, but that position will be thrown into doubt when Mr O'Kane succeeds Nigel de Gruchy as general secretary this Easter.