Margaret Lochrie, chief executive of the Preschool Learning Alliance (PLA), has been urging ministers to reconsider giving parents who send their four-year-old to a playgroup a voucher worth only half the full Pounds 1,100.
She said: "Our members are writing to MPs about this. If there is no more money, there is a problem."
Many playgroups have made it clear they are reluctant to take part in the voucher experiment unless they are given more money. At a recent meeting with PLA leaders, education minister Robin Squire said he wanted to resolve the matter urgently.
Lib Dem education spokesman Don Foster has claimed that the Government can save Pounds 50 million a year if the playgroups' parents receive only a Pounds 550 voucher.
Playgroup leaders, who have 200,000 four-year-olds in their preschools, are hoping for an answer before their annual conference in December.
Whatever the Government's decision, Mr Squire can expect tough questioning from the conference floor. Last year Michael Richardson, head of the Government's under-fives task force, faced a fierce questioning at the PLA's Scarborough meeting. He wooed them with promises and praise, but Mr Squire will find it difficult to do the same.
Meanwhile, Nigel Spearing, MP for Newham South and a former geography teacher, has criticised the Government's under-fives consultation exercise at the end of last year. Mr Spearing said that only four organisations support nursery vouchers out of the 74 the Government consulted.
The four are the Incorporated Association of Preparatory Schools, the National Private Day Nurseries Association, the Playgroup Network and the GM Initiative.
But education minister Eric Forth told Mr Spearing: "Most of the responses to consultation were received before voucher funding for preschool education became an issue for debate."
Julia Bennett, principal education officer for the Association of Metropolitan Authorities, said the problem over the playgroup vouchers was yet another example of the scheme not being thought through.
She sympathised with the PLA's position, but stressed that the cost of nursery education was higher than that of providing child care.