The “burners” are upset about changes to their holiday pay and will down tools from Monday.

Rachelle Wilkins, GMB Regional Organiser, said “The holiday entitlement for the Burners was agreed between the company and trade unions years ago.

“This group of workers have to monitor the gas fuelled kilns continuously over a 24 hour period.  They work 12 hour shifts and cover all bank holidays.

“As part of a reorganisation of shift patterns and terms & conditions in 2011, it was agreed on two separate occasions with management that the Burners would not reduce down to 29 days holiday with the rest of the workforce but would keep their 33 days in recognition of the unique role they undertake at the plant.”

“We have tried to resolve this by every avenue possible with local management, including negotiations with ACAS which took place in Whittlesey on Thursday 4th April.  This group now feel they have no other option but to take strike action from Monday 8th April.

“We have serious concerns that Hanson local management are considering using untrained workers to operate the kilns, workers who have not performed the role for a considerable length of time and have not had any refresher training.”

A Hanson spokesman said: “When we closed our Saxon works at Whittlesey a year ago and consolidated brick production at Kings Dyke we took the opportunity to introduce harmonised terms and conditions of employment for all departments in the works.

“The new terms, which remain generous and are in line with industry standards, were agreed and accepted by the majority of the workforce who also accepted a one-off payment of £1,500 to compensate for any reduction in benefits.

“It is disappointing that, having accepted the compensation payment, a small section of the workforce has now changed their minds.

“We hope industrial action can be avoided but have a contingency plan in place to ensure the factory continues to run and production is not disrupted.”