Exam board staff are set to stage a 72-hour walkout that could disrupt the delivery of thousands of GCSE and A-level results.
Unison said around 180 staff members at AQA's office in Manchester will walk out from July 29 to 31 following a dispute over pay.
Those involved include staff who arrange the setting and marking of exam papers and results nationally, as well as other roles like customer service.
It comes as Britain braces for a summer of discontent after the Tories unveiled a “massive national pay cut” for more than 2million public sector workers.
Railway staff, posties and lawyers had already walked out over pay - and now they could be joined by NHS workers and teachers.
Unison official Lizanne Devonport said the workers have been left with "no other option" but to strike.
"Pay has been falling behind prices for years and 3% isn't a wage rise, with costs spiralling it's a pay cut," she said.
"Things are so bad staff are fearful they will no longer be able to make ends meet.
"Workers only strike as a last resort. They'd rather be doing the jobs that they're proud of.
"They don't want to disrupt students and know how important exam results are to them."
AQA said the average pay increase will be 5.6%, comprising of 3% for all staff, a pro-rata payment of £500 and, for any staff not currently at the top of their pay grades, an incremental increase.
A spokesperson said: "Our priority is always to make sure students get the results they deserve on time - and we have robust plans in place to make sure any strike action won’t affect that. It’s a shame that Unison is claiming otherwise, as this is wrong and only serves needlessly to alarm students and teachers.
"We’re giving our people a pay rise that’s affordable and higher than many organisations, so it’s disappointing that Unison has decided to take strike action. The vast majority of our staff don’t support a strike, as only around 5% of our workforce and well under half of Unison’s own members voted for it.
“Indeed, nearly nine out of ten of our staff have already opted in to our new pay framework and agreed to the pay rise, including many Unison members, so it’s hard to see what this strike is trying to achieve."
