The first ever strike action by teachers over proposed sixth-form closures will be staged next week, TES Cymru has learnt.
Around 40 members of the NASUWT teachers' union will picket Rhyl High School, which is at the centre of an escalating row over potential job losses and the loss of sixth-form education.
Striking teachers look likely to be joined by union colleagues at another Denbighshire secondary - Blessed Edward Jones RC High School - who will be balloted on strike action today.
Catherine Britton, head of the faith school, said she expected that her teachers would vote to walk out, adding that they had her full support.
"Rhyl is being seen as a flagship case. If this (sixth-form closures) is going to happen elsewhere, there will be more protests," she said.
Teachers at both schools are angry about plans to scrap their sixth forms and transfer pupils to a new centre linked with nearby Llandrillo College. It is not certain yet if either school will be forced to close.
But unions warned this could be the first of many strikes over the 14-19 learning pathways shake-up.
There has been growing unease over government policy following last month's announcement of a 7.43 per cent cut in post-16 funding.
Many see the cuts, which will hit small sixth forms worst, as a "covert" way of axeing what are seen as bastions of academic excellence.
Gareth Jones, secretary of the ASCL heads' union, said the loss of funding from sixth forms was already causing problems: "I know of a few schools where there has already been an impact on the breadth of the curriculum they can offer."
Many believe Wales is moving towards a "tertiary-style" system, but without adequate consultation.
Suzanne Nantcurvis, on the NASUWT executive for North Wales, said members were worried about their jobs, but also the future of sixth-form education in Wales.
"We want to work collaboratively with the college, but what we don't want is a takeover," she said. "We also have concerns about who owns contracts for staff. There are a lot of insecurities for teachers at the schools."
There are also other concerns about the introduction of 14-19 learning pathways. Last week, the General Teaching Council for Wales called for a professional body of further education lecturers to be set up as they are increasingly expected to teach in secondary schools under the 14-19 curriculum.
Lecturers in England are represented and regulated by the Institute for Learning, but there is no equivalent body in Wales.
Teachers' unions and fforwm, the body that represents colleges in Wales, believe the Assembly government is "dragging its heels" over setting up a similar organisation in Wales. Sylvia Davies, fforwm's head of public affairs, said lecturers in Wales were being trained using a qualification that was not appropriate for schools: "There is a draft qualification waiting to be approved and my understanding is that they are taking into account schools and young people. But it has been waiting to be approved for some time now."
A spokesperson from Denbighshire county council said the authority remained committed to closing the sixth forms: "Llandrillo College is an outstanding college and we look forward to seeing these plans come to fruition. There has been full consultation with the headteachers, governors and staff throughout the entire process."
The Assembly government plans to hold a three-week consultation on the proposed closures, but a final decision is expected from Jane Hutt, the education minister, before the end of March.
An Assembly government spokeswoman said a letter had been sent to all interested parties. She said it would not be appropriate to comment on industrial action.