Marks & Spencer, Aldi and Lidl have all suspended buying chicken from one of the UK's largest suppliers after an investigation allegedly revealed a string of health and safety breaches.
An undercover reporter working at a West Midlands site of the 2 Sisters Food Group (2SFG) claimed to witness workers tampering with slaughter dates and mixing meat of different ages.
Source codes on crates of meat were also changed, the investigation by ITV News and the Guardian claimed.
The practices can artificially extend the shelf life of meat, and make it untraceable in the event of an outbreak of food poisoning.
When meats of different ages were mixed together, the slaughter date of the newest batch rather than the oldest batch would be used, employees claimed.
Some workers also claimed the chicken that supermarkets reject is sometimes repackaged at the factory and sent out again.
Quality assurance workers told journalists they were intimidated by production managers and worry about being sent home if they try to enforce food hygiene rules.
2SFG was founded in 1993 and now produces one third of all of the poultry products consumed in the UK, and had revenues of £3.1 billion in 2016.
Founder Ranjit Singh Boparan and his wife have built up a personal fortune of £544 million according to the Sunday Times.
The company now has brands such as Fox's Biscuits, Goodfella's Pizza and the Harry Ramsden fish and chip chain in its stable, but poultry is still the company's strongest revenue stream.
It counts supermarkets such as Tesco, Sainsbury's and Aldi as well as M&S and Lidl among its biggest clients, but now several have vowed to suspend their relationship with the firm until the investigation has concluded.
A spokesman for Lidl said: "Lidl UK takes the issue of food safety extremely seriously and we were very disappointed to see the unacceptable standards shown in yesterday's report.
"We immediately launched an investigation with the supplier and can confirm that we will not be sourcing from the site until the investigations have been satisfactorily concluded."
Aldi added: "We have suspended supply from this site while we carry out an urgent investigation into these allegations.
"We expect all suppliers to adhere to the highest possible food hygiene and traceability standards at all times."
M&S said it had also suspended business with 2SFG, pending the outcome of an investigation.
A spokesman said: "As a precautionary measure, all fresh chicken that is supplied directly from this site has been removed from our shelves today."
Tesco and Sainsbury's have both issued statements saying they were investigating the allegations.
The Food Standards Agency (FSA) said that it had found no evidence of breaches during an inspection of the plant following the Guardian and ITV News' allegations on Thursday.
But it said it was still reviewing evidence, saying: "If any incidences of non-compliance are found we will take prompt and proportionate action with the business concerned, working closely with the local authority."
It said in a statement: "We would urge ITN and the Guardian to share any additional evidence, including witness statements, that would inform our investigation.
"This particular cutting plant is regularly audited by the FSA and they are also subject to unannounced inspections. The FSA urges anyone with information for this investigation to contact them."
2SFG said in a statement that it viewed the allegations "extremely seriously", but added: "We have not been given the time or the detailed evidence to conduct any thorough investigation to establish the facts, which makes a fulsome response very difficult."
It said it was regularly subjected to unannounced audits by the FSA and other food hygiene organisations.