Asda staff will take part in a mass demonstration outside its head office today over claims the grocer is “bullying” workers into signing new contracts.

Members of the GMB union will march from Leeds city centre to the supermarket giant’s head office on Great Wilson Street at midday to rebel against the new terms.

Asda put around 3,000 employees into consultation in April over proposed changes to their contracts, which would see their basic hourly rate of pay increase to £9 an hour.

However, the new deals also strip out paid breaks and would class bank holidays – other than Christmas, Boxing Day and New Year – as normal working days.

The contracts also include an increase in the ‘premium’ night shift pay rate but have shortened the length of these shifts.

The consultation period ended earlier in the summer, but Asda has not confirmed how many people signed the new contracts.

MPs have voiced concerns over the new contracts and claim they would leave staff worse off.

GMB said 93% of its members who work at Asda opposed the “unacceptable” new contracts.

Asda is one of the last major retailers to implement such changes to contracts for its shopfloor teams.

Grocery rivals such as Tesco and Sainsbury’s, along with the likes of Marks & Spencer and B&Q, have all ushered in similar changes in recent years.

GMB said it has received reports of managers “using bullying and threatening behaviour” against Asda staff in a bid to get them to sign the new contracts.

It alleged that one manager went “uninvited to the home of members who are suffering terminal illnesses”, while others are said to have threatened to withhold holidays and sick pay if staff did not agree to the new terms.

Asda is understood to be investigating the claims.

A spokesman for the supermarket giant said: “The retail sector is undergoing significant change and it is important that we are able to keep pace with these changes. The overwhelming majority of our colleagues have signed onto the new contracts and while we appreciate that some of our colleagues find the changes more unsettling, we do not want anyone to leave. We have been clear that we understand colleagues have commitments outside of work and will not be asking them to constantly move the time they work, their days or departments. Any changes will be with at least four weeks’ notice.

“This contract is about increasing the take-home pay of more than 100,000 retail colleagues, through an investment of more than £80m, and ensuring that everyone doing the same job is on the same terms and conditions.”

GMB regional organiser Keith Dixon said: “GMB feel the company’s contract would result in a devastating impact upon the work-life balance, security and income for our GMB members within Asda.

“Asda need to understand the value of their dedicated workforce who have for many years grown Asda to be a multibillion-pound profitable business.

“It is despicable that a company the size of Asda would treat their colleagues in such a way.

“It is time that Asda realises that they have lost the respect and support of their workforce and agrees to meet with GMB to negotiate better terms on behalf of the members.”