The CBI sees the worth of employment-related Diplomas
The employers' organisation the CBI says government plans for Diplomas in academic subjects in England are "an unnecessary distraction".
It says employers back Diplomas related to employment sectors - but the ones in humanities, languages and science could result in a two-tier system.
They fear private schools would pursue GCSEs and A-levels, with the state sector turning to Diplomas.
The government says it is surprised at the CBI's negative response.
But the Tories say ministers are putting ideology before what is needed.
In a statement, the CBI said that following extensive consultation with businesses across the country, it was urging the government to think again about "its over-ambitious plans for a new wave of academic Diplomas".
It should instead "concentrate on making sure GCSEs and A-levels give young people the skills and knowledge to succeed".
Reiterating its strong support for Diplomas for industries such as hospitality or engineering - as a "parallel qualification" to GCSEs and A-levels - the CBI says they were created with substantial business input.
But the statement continues: "Employers are worried about the more recent proposals in the government's Diploma strategy to introduce a new range of academic diplomas in humanities, languages and sciences.
"CBI members fear they would not have any greater value to young people or to employers than the existing GCSEs or A-levels, and would instead be an unnecessary distraction."
'Raft of changes'
Other concerns highlighted in the CBI response included the workload for schools.
"Over the next few years, schools and colleges are already being expected to manage a raft of changes.
"These include delivering new functional literacy and numeracy modules and new GCSE and A-level curricula, together with the extra demands of keeping young people in education or training till 18.
"Going ahead with these plans without tackling concerns, employers fear, could lead to a fractured two-tier education system with private schools opting for GCSEs and A-levels, or even the International Baccalaureate, while state schools use Diplomas."
Diplomas - which are beginning to be taught from this September - are available at three levels of attainment, which the CBI wants simplified to two - one for 14 to 16-year-olds, and one for 16 to 18-year-olds.
CBI director general Richard Lambert said: "Given the increasingly global challenges the UK faces all sides accept we cannot simply protect the status quo in the education system, but make sure it is evolving.
"However employers understand and value GCSEs and A-levels and firmly believe these should remain a cornerstone of the education system."
England's Minister for Schools and Learners Jim Knight said: "I am surprised at this negative response from the CBI on our three subject-based Diplomas, given that Richard Lambert shared the platform with Ed Balls and myself when we launched them last October.
"The CBI were also represented on the expert group which approved our qualifications strategy."
Mr Knight said the mix of theory and applied knowledge the Diploma offered would help boost the number of young people studying science and languages, by bringing these subjects to life and giving students the skills employers wanted.
Shadow schools secretary Michael Gove said: "By pushing ahead with plans for academic Diplomas the government risks undermining the existing diplomas and it threatens the future of GCSEs and A-levels."
The director general of the Russell Group of research intensive universities, Dr Wendy Piatt, said the Diploma was a way to expand higher education to students from a wider range of backgrounds.
"We particularly welcome the introduction of a science Diploma as we are still concerned about the low proportion of students - largely from state schools - taking science A-levels."
She added however that universities were still assessing "the academic rigour and general suitability of the Diploma as a route to higher education".
The leader of the National Union of Teachers, Christine Blower, said: "The CBI has consistently taken a profoundly pessimistic view that young people at an early age should be sorted into vocational and academic tracks of learning.
"A lesson for the government should be that it ought to be careful about the friends it chooses."