Asda has slammed union bullying tactics and misrepresentation in an on-going staffing row at the supermarket chain.

The GMB union has said Asda would bus workers in illegally and it was preparing to film staff coming into work to prove agency staff were being used illegally to force an end to the strike.

A spokesman for the chain said: “We use agency support all year round. There are no more agency workers in our business today than there were this time last year. We are not going to break the law. We have no intention of using agency workers to break the strike.

“We have no intention of bussing in anyone who isn't legally entitled to work. We are making preparations to bus colleagues into work. Many have expressed concerns about being filmed crossing the picket line. Colleagues are calling us saying the GMB's plans are equivalent to electronic bullying - so we're doing all we can to ensure anyone who wants to work can do, without having their number plate recorded by the GMB.”

The GMB has pledged to greet workers who boycott the strike with the words: “Smile you are on camera when you cross this picket line”.

The strike was announced following disputes about union representation in Asda’s depots.

The chain is insistent that shoppers will not be affected by the five-day strike that is due to start on Friday.