With only four months to go before ministers receive a final blueprint for reform of 14 to 19 education over the next 10 years, business representatives have still to endorse the proposals.
The Confederation of British Industry has already criticised the plans to replace GCSEs and A-levels with a diploma being drawn up by Mike Tomlinson, the former chief inspector.
Mr Tomlinson, who chairs a government task force which is devising the diploma, has written to the chief executives of all FTSE-100 companies in an attempt to win them over.
However, there were rumblings of discontent this week from a body which works with 200,000 firms across England.
Sources at the national Education Business Partnerships network said that many employers were struggling to understand draft plans for a four-level diploma, set out in a highly technical 100-page report in February. Many businesses, they said, also felt they had had little input into the diploma proposals, which had been written largely by educationists in language that lay people found difficult to understand.
In its official response to an interim report by the Tomlinson group, the network praised the task force's aims.
It warned there was a danger that the diploma could be too complex, however, and said that employers should have a much greater involvement as the plans were developed.
Mike McCann, chief executive of the network, said: "A more pro-active approach to organisations such as ours, which are in touch with 200,000 employers, would be helpful."
Mr Tomlinson has tried to involve representatives from all sectors of education and training. Business people sit on the task force, which also has an employers' sub-group.
Ian Ferguson, chairman of computer firm Data Connection and a task force member, said that both the CBI and the British Chambers of Commerce were consulting members on the Tomlinson review.
"This is probably one of the widest consultations involving employers that there's ever been," he said.The criticisms could be highly damaging to the diploma, as the support of employers is crucial to the success of reforms, which envisage a transformation in vocational education.
The controversy comes as headteachers called on Mr Tomlinson to make modern languages compulsory for the intermediate diploma, set at GCSE-level.
Under the present plans, only maths, communication and information technology would be required subjects at intermediate level.
The Secondary Heads Association wants study of languages, arts, humanities, religious education and physical education made compulsory.
The National Union of Teachers has also said that a requirement for all students to gain the equivalent of at least a grade C in maths and communication to achieve the intermediate diploma is too ambitious.
Consultation on the second draft diploma report finished officially last week. The task force will produce final recommendations for ministers in September.
Wales 2004 Supplement 10