Ambitious plans to transform post-16 education are causing "significant concerns" to teachers - including the potential loss of jobs - the Assembly government has been warned.
The so-called transformation agenda is progressing too quickly and without proper consultation in some areas of the country, according to teaching union evidence to a cross-party committee of AMs.
All 22 Welsh local authorities, along with FE colleges and private training providers, were asked to submit detailed proposals to transform their post-16 provision in 2008.
They were challenged to "set aside traditional, narrow institutional arrangements" and plan collectively to improve education and skills while getting the best value for money.
Last week Education Minister Leighton Andrews praised those who had "risen to the challenge" and said that 70 per cent of the proposals would be implemented by this September, exceeding the government's original target of 60 per cent.
But while some plans have progressed smoothly, others have faced difficulties and opposition.
Rhondda Cynon Taff's proposal to close its school sixth forms and replace them with bilingual tertiary colleges has come under fire from Plaid Cymru and teaching union UCAC, which claim it would downgrade Welsh-medium education.
Plans to scrap sixth forms in Merthyr Tydfil and Blaenau Gwent have also faced staunch opposition from politicians, unions, teachers and pupils.
In their evidence to the Enterprise and Learning Committee inquiry, the teaching unions said the agenda had focused too much on structures and not enough on standards.
Despite repeated assertions from the Assembly government that the policy does not take a "one-size-fits-all" approach, the unions still suspect a hidden agenda towards tertiary education systems.
There were also claims that in some local authorities there has been little or no proper consultation with schools and teachers.
Rex Philips, Wales organiser of union the NASUWT, repeated his concern that Welsh education could be facing a "doomsday scenario" because proposals have been progressed on economic, rather than educational terms.
He said: "The livelihoods and careers of teachers, and other school-based staff, are being viewed as collateral damage in the pursuit of the lowest- cost option for the provision of post-16 education."
Heads' unions NAHT Cymru and ASCL Cymru called for the agenda to be slowed down so a consensus could be reached in each local authority before plans progress.
Several committee members said they were "taken aback" at the strength of concern from the unions, but Mr Andrews distanced himself and the Assembly government from some of the criticisms.
He said: "At no stage have we adopted a `one-size-fits-all' approach. Instead we have asked local authorities to come up with their own ideas.
"I think some of the concerns being raised are issues I'm familiar with. But we (the Government) are not the employers - the providers are. I don't think it's the role of ministers to build relationships between unions and providers. It's not our role to solve every problem on the ground."
Original paper headline: Unions: careers will be `collateral damage' in post-16 overhaul