The Scottish Qualifications Authority has been threatened with an ultimatum to reduce the "enormous" marking burden of new qualifications by Christmas, or face a teacher boycott.
The SQA was the lightning rod for anger at the annual gathering in Perth last week of Scotland's biggest teaching union, the EIS, where delegates complained of the workload driven by new assessment requirements.
Although the authority has promised improvements in the next three years, EIS general secretary Larry Flanagan warned that far more urgent action was needed.
He linked new assessment practices to a headline drop in literacy standards over the past two years, during which "secondary teachers have worked until they almost dropped" to implement new qualifications "against a timetable which was too short and where the SQA failed to provide the support which schools deserved".
The Highland and West Dunbartonshire EIS branches won unanimous backing after demanding a ballot by December on industrial action, "amounting to a boycott of cooperation with SQA, including the marking of unit assessments [of National 5 and Higher] until such time as the SQA reduces the enormous burden and reforms the nature of internal assessments for all courses".
The SQA would need to react before the EIS council meets in September to assess progress of conference motions.
Highland teacher Alison MacDonald told delegates: "I was delighted to hear Larry Flanagan say that he had put the SQA on two months' notice of the need for reform, and hope that this invokes a speedy response, in which case there will be no need to invoke the terms of this motion in December."
She decried the "appalling bureaucracy" of unit assessments of "dubious educational validity", and said the SQA had "grossly abused the professional trust of teachers".
West Dunbartonshire teacher Michael Dolan said the SQA had "dropped whole sections of the school population from the assessment process" - a reference to qualifications such as National 4, which have no external assessment - and "dumped the workload onto teachers".
He cited SQA figures showing that S3 and S4 pupils sat more than 510,000 external exams at Intermediate and Standard grade levels in 2012, but by 2014 the number of equivalent exams had fallen to 310,000 - with much of the responsibility for assessment being shifted to teachers.
An SQA spokesman said the authority was "very conscious" that teachers needed support to implement the new qualifications, and said it was offering this help in various ways, as was Education Scotland.
He said that the SQA had "reflected on lessons learned from the 2013-14 session" and actioned the recommendations of the recent Curriculum for Excellence "reflections group" report.
Changes had been made to the verification process for new qualifications, he added, and the SQA had helped to reduce workload by cutting the number of verification rounds from three to two. Unit assessments had also been changed, he said, and more amendments were planned for 2015-16.
Anger with the SQA was a recurring feature of the three-day conference, where strike action over pay was also threatened. Outgoing president Tommy Castles likened the authority to Doctor Who villains the Daleks, because of its perceived intransigence over assessment and the fear it instilled.