They fear that disadvantaged groups of young people - including the long-term unemployed, pupils with special educational needs and immigrants with language problems - could suffer.
They voiced their fears as regional offices of the Department for Employment negotiated the break-up of the local authority-run service, and it emerged that councils were being split up or hybrid new areas created.
Private companies are almost certain to take over part of Buckinghamshire, while Stockport and the High Peak district of Derbyshire are to be merged to create a single authority.
The first contracts will not be awarded until April, but it is already clear that commercial outfits are front-runners to take over the service in at least four LEAs. They are also competing directly against councils in two others.
Business leaders and councillors have criticised delays in the reshuffle and the lack of information on how bids are selected and contracts awarded.
The Institute of Careers Guidance has now warned of tensions between commercial viability and meeting targets set by Government on the level of service to students.
Mike Clark, president of the IGC, said: "Where there are tensions, there are worries that commercial interests might be the first priority."
Private companies interested in taking over the careers service include Cheshire-based Nord Anglia Education, which runs 20 independent schools in the UK, has its own Office for Standards in Education unit tendering for inspections, and is a leading provider in English as a foreign language.
It is the preferred bidder for the new StockportHigh Peak service and is currently competing forcontracts against Solihull and Northamptonshire LEAs.
Kevin McNeany, chairman, said targets would be met to the satisfaction of the Department of Employment, which awards the contracts, and added: "They will not just be met but also fulfilled to quality standards."
Councillors in Stockport learned on the day they were praised by the Government for running a successful careers service that they had lost it to Nord Anglia, and have now called on MPs to raise questions in the House of Commons.
In Solihull, the Chamber of Commerce has accused the Department of Employment of endangering the careers service by once again postponing the decision over who is to run it.
John Hart, president, said: "The Government is trying to encourage the involvement of business in many of these joint initiatives and a great deal of time and energy is being spent in work alongside local partners, only to be continually frustrated by Government decision makers."
Careers Enterprise, a joint venture between Surrey Careers Ltd and Partnership UK, is the preferred bidder for the service in Kent and part of Buckinghamshire.
It looks certain to take over the area serving Aylesbury Vale and Milton Keynes at the end of March.
Crispian Graves, education chairman for Buckinghamshire, said: "We were told that the department's preference was to retain a single, countywide service . . . since that is the service provided at present, we felt well able to meet its wishes. It, therefore, comes as a great disappointment to find that this has not happened."
A Reading-based company called Compass Education Services is likely to take over the service in Berkshire and Oxfordshire.
A consortium comprising Calderdale and Kirklees LEAs, the Calderdale and Kirklees TEC and Huddersfield University will take over the service for that area.