A crunch meeting is to be held after teachers threatened to boycott new assessment arrangements for pupils.
Education union the NASUWT Cymru warned in March 2005 that scrapping Sats at key stages 2 and 3 in Wales would lead to an alternative assessment system that would be even more bureaucratic.
A survey of 800 members of the union in Wales has revealed that more than 94 per cent would consider a boycott of the new teacher assessment arrangements, recommended last year following consultation.
Now NASUWT members will be meeting with representatives from the Assembly government's department for children, education, lifelong learning and skills (DCELLS) next week to discuss the issue.
Their concerns centre around a March 2007 Assembly government document, Future Assessment Arrangements for Key Stages 2 and 3.
The document recommends a new focus on internal assessment, carried out by teachers and moderated by feeder schools at KS2. External accreditation will be used for moderation at KS3. The new arrangements are due to come into force this spring or summer.
The document was published following consultation with the teaching profession and unions.
But union leaders say teachers will have to take time out for assessment and moderation work at the expense of their core teaching role, and this could add up to 15 hours to their working week.
Since Sats were abolished in Wales for 11-year-olds in 2004 and 14-year-olds in 2005, it has been left to individual schools to decide how to assess pupils.
Now union leaders are calling on Wales's education minister Jane Hutt for an urgent review of teacher assessment. They want to see a new streamlined national system that will cut out red tape.
NASUWT Cymru organiser Rex Phillips said: "If DCELLS is not prepared to have this system following the meeting, then a boycott is the only way forward."
More than nine out of 10 NASUWT members surveyed have called for a simplified system, and a similar proportion say they believe the new arrangements will become a bureaucratic nightmare.
Worries have already been raised following pilot schemes using the new recommended system, with reports of increased workload taking its toll on tired teachers.
Chris Keates, general secretary of the NASUWT for Wales and England, said: "Bogging teachers down with paperwork won't raise standards in schools.
"Unless there is a commitment to resolve this matter quickly, it will be difficult to see how a boycott through industrial action can be avoided."
Rhys Williams, National Union of Teachers Cymru spokesman, said his union would possibly back the NASUWT action if the assessment arrangements meant teachers were always putting in extra hours.
Mr Williams added: "We think teacher assessment is a good thing but are concerned about the workload implications. It could mean up to 15 extra hours a week. We would certainly respect any action being taken by our colleagues in the NASUWT."
Brian Lightman, president of the Association of School and College Leaders Cymru, supported the plan to make the assessments "more workable".
He suggested one possible solution would be to make a small number of teachers in a school "chartered assessors" in charge of overseeing this to free up time for other staff.
An Assembly government spokesperson confirmed the meeting is taking place and said officers would be happy to hear the NASUWT's views on the matter, adding that teachers' views were "very important" for successful assessment arrangements.