Staff at an exam board are set to take strike action during both A-level and GCSE results periods.
AQA staff were already due to strike next week but have now scheduled further dates later in the month for industrial action, Unison said.
The union said the action is planned as part of a long-running dispute regarding pay and fire and rehire threats to staff.
But AQA accused Unison of making “scaremongering claims”, and said it had “robust contingency plans in place to ensure that industrial action has no effect on results”.
Some 180 workers, including staff in customer services who Unison said would normally take calls from schools, parents and pupils on results day, will take action from August 24 until 28.
GCSE results are set to come out on August 25.
Workers had already been set to strike from Wednesday to the following Sunday – coinciding with A-level results being published on Thursday August 18.
Exam board employees are also striking from Friday until Monday. This follows industrial action at the end of July.
Unison North West regional manager Vicky Knight said: “Last year staff were given a meagre wage rise. AQA employees are struggling to make ends meet and simply cannot afford to accept the miserly pay award on offer.
“On top of this, AQA is threatening dismissal and re-engagement if staff don’t accept.
“Threatening the dreadful practice of fire and rehire is no way to make progress in a dispute. AQA managers must come back to the table and discuss a fair resolution.”
An AQA spokesman said: “These are the same, scaremongering claims that Unison keeps making, and that we’ve already proved wrong: we’ve set all our grade boundaries, and yesterday we sent A-level and AS results to Ucas as we do every year. So everything is on track, and we wish all our students well for the results they’ll receive on August 18 and 25.
“Unison’s actions to deliberately target students like this are pointless and completely ineffectual. It won’t stop us from delivering the exam results our learners so richly deserve or supporting everyone afterwards.
“We have robust contingency plans in place to ensure that industrial action has no effect on results, and our records show that only 4% of our total workforce took part in that industrial action – the remaining 96% are absolutely committed to never letting our learners down.”
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