Animal welfare campaigners have staged protests at more than a dozen Morrisons supermarkets across the country.
The demonstrations were led by one of the retailer’s own employees, who claims he is facing disciplinary action after highlighting allegations about the chickens it sells.
Earlier this month, an investigation accused one of Morrisons’ main suppliers of rearing “FrankenChickens” – birds genetically engineered to grow bigger and faster than they naturally would.
The Open Cages charity alleged it saw chickens suffering in cramped conditions at four intensive farms, and some birds were “completely or almost unable to walk”.
Doug Maw, who works at the supermarket’s Bognor Regis branch, claims the retailer told him that his social media posts about the issue were “inappropriate”.
Protests took place at Morrisons stores in London, Liverpool, Manchester, Bristol, Reading, Sheffield and Dundee.
Mr Maw said: “Morrisons has made me feel unwelcome as a member of staff and questioned my commitment to the company for putting my values first.
“I believe we all have a responsibility to hold the companies we work for to account, and encourage them to do better.”
Earlier this year, Morrisons denied that it had silenced Mr Maw – telling The Independent that it encourages discussion and debate among colleagues.
“In fact, we encouraged him to post his views on Morrisons’ general colleague Facebook page, which hosts a range of discussions on a broad array of topics,” she added.
And in response to the Open Cages investigation, the retailer said: “We care deeply about animal welfare and require all our suppliers to maintain the highest standards. We have asked Cranswick [the supplier] to conduct a full investigation and report back to us.”
According to campaigners, more than one billion chickens are raised and slaughtered for their meat in the UK every year.
Animal welfare groups claim that the vast majority of them are bred to grow at an unnatural speed that means they reach their slaughter weight in a matter of weeks.
In some cases, chickens can suffer painful lameness and heart attacks because of this fast growth.
Morrisons is being urged to sign the Better Chicken Commitment, a policy that prohibits the use of fast-growing breeds and aims to ensure chickens are reared with natural light and more space.
So far, Marks and Spencer and Waitrose are the only British supermarkets that have signed the commitment.
Cranswick – the chicken supplier that featured in the Open Cages investigation – has apologised for the footage.
A spokesperson said: “We have been made aware of footage of our farms, filmed by Open Cages, following on from a number of separate incursions.
“The film shows a small number of our chickens suffering on farms operated by Cranswick and these birds should have been removed as part of our standard high welfare procedures.
“The team at Cranswick would like to apologise for the recent footage. We have investigated this thoroughly both internally and with the support of unannounced external audits. Whilst we are confident that the occurrences are isolated we have identified procedural improvements to our farming system that have been implemented to significantly reduce the likelihood of an issue occurring in the future.”
They added: “We are extremely proud of our long-standing reputation for maintaining excellent standards of animal welfare across the business, and this will always be our top priority.
“All of our chicken farms operate to the accredited standards of the Red Tractor mark and have a long-standing track record of excellent independent audit results. We also frequently review and invest in projects that further enhance welfare such as our recent introduction of in shed hatching for all of the chickens we grow.”
Sky News has contacted Morrisons for a comment.