Trade unionists are calling for non-contact time for teachers in Wales to be postponed until sufficient funding and staffing can be found to implement it properly.
Members of UCAC, the Welsh-medium teachers' union, are due to debate the proposal at their annual conference, being held today and tomorrow in Aberystwyth.
Gruff Hughes, the union's deputy general secretary, expects the motion, directed at the Welsh Assembly and submitted by members in Powys, to garner significant support.
But the call, if backed, is likely to fall on deaf ears in Cardiff and London. Planning, preparation and assessment (PPA) time is a contractual requirement from September, and other classroom unions have threatened legal action against schools and headteachers who fail to deliver 10 per cent non-contact time.
UCAC, like the National Union of Teachers, did not sign up to the agreement. Around 650 of UCAC's 4,790 members are heads or deputies. Mr Hughes said the Powys motion reflected widespread unease about the reform.
"There is a great concern about whether we will be able to uphold standards. Members don't feel adequate training has been given to classroom assistants, and Welsh-medium schools have problems finding Welsh-speaking support. One school in Gwynedd is going to provide PPA - but by having bigger classes."
Another motion, from Rhondda Cynon Taf and Merthyr Tydfil, calls for more Assembly cash to avoid heads raiding other parts of the school budget to deliver the workload reforms, and to ensure teachers, rather than classroom assistants, cover PPA.
A spokesperson said the Assembly government did not comment on union conference motions. It has allocated pound;161 million to 2007-8 for workforce reforms and is committed to implementing the agreement.
Other motions on the agenda concern Welsh second-language teaching, pensions and skills tests.