Just over half (58%) of union members that took part in a recent ballot said they were prepared to take industrial action, while 68% were prepared to take action short of going on strike, Paddy McNaught, an organiser at trade union Unite, told FoodManufacture.co.uk.

"We had a meeting last Thursday (September 9) and the decision was taken to take industrial action for a week, starting Monday. We have informed the company of our intention this morning.”

Staff had been offered a 2% increase in basic pay but were “looking at something more in line with the RPI (retail price index)”, he added.

The factory employs about 350 staff. McNaught has not revealed how many union members voted in the ballot.

A Vion spokesman said: "Vion has been informed this morning by trade union Unite that five days of discontinuous strike action is planned by its members, to commence at Vion Llangefni from next Monday.

"Vion has offered a pay award of 2%, and is disappointed with the decision to take industrial action. The business will continue to focus on providing uninterrupted supply to its customers."