Headteachers have threatened to challenge their union if its council votes to remain within the workload agreement this week.
Fierce debate was expected yesterday as National Association of Head Teachers' council members, who are predominantly primary heads, discussed how to act on their conference's decision that staying in the deal should depend on the Government announcing "clear, adequate and direct funding" by the end of the year.
David Hart, NAHT general secretary, said pulling out would be "catastrophic" for the association but he was confident that there would be enough money and that the council would vote to stay in.
However, a TES telephone poll of 28 of the 46-member council indicated that it could be a close call, with 10 saying they were likely to vote for withdrawal, 12 to stay in, and six undecided.
Council members at the centre of the withdrawal call said if the vote went against them, they had enough local branch support to trigger an extraordinary NAHT general meeting, which would have the power to overturn the decision.
Sid Wilcocks, council member for Dorset and Wiltshire, said: "Colleagues are saying enough is enough, we have not got the money and are asking what the NAHT is doing about it."
But Mr Hart said that to hold such a meeting was a "recipe for splitting the NAHT asunder". The debate is over whether schools will be able to deliver the final and most expensive phase of the workforce deal. This part of the deal would guarantee teachers 10 per cent planning, preparation and assessment time from September 2005.
During stormy discussions at the association's May annual conference delegates defied Mr Hart and set the year-end funding deadline.
In July, the Government announced a minimum 5 per cent per pupil funding increase for primaries in 200506, compared to 4 per cent for secondaries, which it said left no excuse for not implementing the agreement.
Mr Hart said this week that a substantial majority of schools would get increases of more than 6 per cent with extra money for small and rural schools. He said the NAHT had negotiated a "pretty good package".
However, several council members who planned to vote to stay in the agreement said they were only doing so because it was pointless withdrawing from a deal that would go ahead without them.
Tim Benson, east London national council member, said it would cost his school, Nelson primary in East Ham, up to pound;150,000 to implement PPA time. According to local authority estimates, he only expects to have pound;40,000 extra.
The shortfall was likely to mean cuts to building maintenance and teaching resources which could not be sustained long-term. His plan to give teachers somewhere quiet to conduct their PPA time was now a non-starter.
Council members also revealed that many opposed the idea of using support staff to cover classes, a major part of the agreement.
David Gray, member for Devon and Cornwall, said: "By teaching, we mean a teacher in front of the class and we haven't got the money to pay for it."
Monica Galt, council member for Manchester and Cheshire, said she had never known heads so worried about an issue.
At a training meeting on PPA time organised by Nottingham council last week, all 40 heads attending expressed concerns about a lack of funding, according to Philip High, head of Radford primary and a National Union of Teachers member.