The future of school sixth forms has been put in doubt following an Assembly government move to back tertiary education, it has been claimed.
Ministers announced a decision to give more than pound;110 million to three major projects, including further education colleges in Merthyr Tydfil and Blaenau Gwent, which will result in eight sixth forms being axed.
Critics have attacked the move because public consultations over the plans are still ongoing. Fears have been raised that dozens of jobs could be at risk as similar projects are considered across the country.
Teaching union NASUWT said that last week's decision showed a "breathtaking disregard" for the school workforce.
The proposals have been driven by the Assembly government's transformation policy, which aims to improve post-16 education while achieving better value for money.
Wales' 22 local authorities have submitted proposals for change, with several looking at tertiary systems.
The proposed Merthyr Tydfil learning quarter would include a new tertiary college and university building, while the Blaenau Gwent learning works, based on the former Ebbw Vale steelworks site, would provide a state-of- the-art centre for all post-16 education.
Both schemes are promising increased access to academic and vocational learning and a greater choice of courses, but four sixth forms in each local authority will be scrapped if the plans go ahead.
Chris Keates, general secretary of the NASUWT, said: "The question is: are these proposals about providing greater opportunity and choice or is this about continuing to provide education on the cheap in Wales?
"These proposals signal the end of school sixth form provision in the heads of the valleys and raise the very real prospect of whole-scale teacher and support staff redundancies."
A consortium of secondary heads in Blaenau Gwent has also come up with its own set of proposals to establish an independent sixth-form college staffed by teachers from across the borough and overseen by an independent governing body.
Brynmawr Foundation School, which has the largest sixth form in Blaenau Gwent, with 230 pupils, could lose up to 15 members of staff if the council's plans go ahead.
Headteacher James Retallick, said: "We feel that under the local authority's current proposals there will be less choice for young people."
The Assembly government denied that it was pre-empting the outcome of the consultations by announcing the funding.
A spokeswoman said: "The funding has been agreed in principle subject to the outcome of statutory consultations in Blaenau Gwent and Merthyr Tydfil."
A spokeswoman for Blaenau Gwent Council said: "We see all our teaching staff as a tremendous resource. They have been, and are being, fully consulted."