Workers who make Jacob’s Cream Crackers and Twiglets go on indefinite strike on Monday in a row over pay.
The GMB Union said more than 750 staff at Jacob’s Biscuits factory at Aintree, Merseyside, will walk out “every single day until bosses agree to negotiate”.
National officer Eamon O’Hearn said: “These workers are rightly angry – they put themselves on the line to keep the company going during the pandemic.
“Now they need some help to get them through the cost-of-living crisis, but it’s falling on deaf ears.
“Jacob’s workers will now be on strike 24 hours a day, seven days a week until the company comes back to the negotiating table.”
Pay negotiations have dragged on for more than a year, according to union sources.
It is understood employees have been offered 4.25% rises - even though inflation is running at 10.1%.
Limited industrial action began in September.
The GMB is thought to have asked for a 10% increase so its members’ real wages are not cut.
But the firm, which makes Twiglets and Mini Cheddars 'Nibbles' as well as 14,000 tons of Jacob’s Cream Crackers every year, is said to believe such a hike would be unaffordable.
A spokesperson for Jacob’s parent company, London-based Pladis Global, said: "We regret that the GMB has decided to take this course of action, despite all of the efforts we have made to reach an agreement with the union.
"However, we want to reiterate that our door remains open to the GMB for further discussions with their representatives."
- This story was updated after publication to clarify that Twiglets, Cream Crackers and Mini Cheddars Nibbles are made in the Aintree factory, but not Mini Cheddars or Jaffa Cakes.
