Three of the UK's major supermarkets have launched investigations into their chicken supplies after an investigation uncovered alleged hygiene failings at factories.
The Guardian reported specific allegations such as a factory floor flooded with the guts of chickens and carcasses coming into contact with workers' boots and then returned to the production line.
It said the allegations related to two of the largest UK poultry processors, 2 Sisters Food Group and Faccenda.
Both companies denied the allegations to the Guardian, but 2 Sisters reportedly told the newspaper that it did not stop the line when a breakdown led to feathers, guts and offal piling up because it had to consider the welfare of chickens waiting in crates to be killed.
The newspaper said its report was based on undercover footage, photographic evidence and information from whistleblowers over five months relating to industry hygiene standards to prevent the contamination of chicken with the campylobacter bug.
Tesco, Sainsbury's and Marks & Spencer confirmed they had launched investigations into their chicken sources over the last week.
The most recent figures from the Food Standards Agency (FSA) suggested that 65% of raw shop-bought chicken was contaminated with campylobacter, the most common identified cause of food poisoning in the UK with symptoms including diarrhoea and stomach cramps.
Although cooking chicken properly kills the bug, it is responsible for more than 300,000 cases of food poisoning and 15,000 hospitalisations a year in England and Wales.
A Tesco spokeswoman said: "Providing safe food is our first priority, so we take these allegations of poor practice against one of our suppliers extremely seriously, and have launched an immediate investigation.
"Customers can be assured that we conduct our own stringent quality checks on fresh chicken received from suppliers before it is placed on shelves, so we can be confident that it meets our very high quality and safety standards."
M&S said in a statement: "We take food safety very seriously and regularly audit all of our suppliers to ensure they meet our strict codes of practise.
"We do not tolerate any alleged breach of our standards and have launched an immediate investigation into these allegations.
"This is an industry issue that we are working with the FSA on and leading the industry on a comprehensive plan to eliminate campylobacter.
"We've provided advice for customers, launched new packaging for chicken and funded trials and projects on reducing campylobacter - all of which is independently monitored."
The Food Standards Agency (FSA) said it was aware of the allegations and would be raising them with the companies concerned.
On Wednesday, FSA chief executive Catherine Brown asked the FSA board to reverse a previous decision to publish campylobacter rates for named supermarkets and processors every quarter.
The board heard there were now concerns that the sample size for one quarter's data was insufficiently large to be statistically robust.
The FSA saidt: "The FSA is committed to publishing the full results from its survey of campylobacter on shop-bought chickens, including names of retailers and processors.
"However, quarterly results cannot be interpreted in a meaningful way, so breaking results down by retailer and processor at this stage could mislead consumers.
"The FSA board agreed with this position but called for the final results to be delivered sooner than previously planned.
"The FSA is now considering how to revise the survey sampling so that full results can be delivered more quickly.
"The first quarterly results will be released as planned without company names in the next few weeks."
A Sainsbury's spokeswoman said: "Customers rightly expect our food to be of the highest safety standards and can be confident in the safety of products bought from our stores. We perform regular independent and in-house checks to ensure these standards are met and are investigating these allegations with 2 Sisters.
"All of our chicken products are labelled with cooking instructions and clear food safety advice."
Faccenda Foods managing director Andy Dawkins said: " Faccenda Foods fully stands by all of our responses to the Guardian's investigation.
"At Faccenda Foods, we recognise the food safety challenge posed by campylobacter and the concerns of consumers in this area. Through our campylobacter action plan, Faccenda Foods continues to invest significantly across the whole supply chain to address this top priority issue. Our investment in current projects to tackle campylobacter is in excess of £1 million.
"Our action plan has been proactively shared and acknowledged with the FSA and our customers, focusing on three key areas - farm biosecurity, interventions in our factory operations and improved food safety in the kitchen. We have further improved biosecurity arrangements in place at all our farms working to revised Red Tractor standards. We also continue to invest in testing for routine surveillance as part of our risk assessment programme. We have committed significant resources to the development of innovative factory interventions to reduce campylobacter and will move to full-scale in-line trials later this year.
"Any change in our process will, where possible, be independently validated and our results shared with the FSA Joint Working Group on campylobacter. Again, we will use our testing programme to monitor progress throughout this period.
"Finally, we have been a leading contributor to the FSA Joint Working Group on campylobacter reduction and continue to support this unique collaborative approach which has made a significant contribution to overall progress across the industry. Faccenda Foods is fully committed to a programme of process and product improvements and believe these will result in real improvements in food safety for consumers."
In a statement on its website, 2 Sisters Food Group said: "The allegations about our processing sites at Scunthorpe and Llangefni made in the (Guardian) article concerning our business and our management of campylobacter are untrue, misleading and inaccurate. There is no campylobacter contamination or problems at our sites, as confirmed by multiple independent external audits and our own rigorous testing.
"We strongly deny and defend ourselves against these allegations. Our company's heritage is steeped in the poultry sector. We are extremely proud of this heritage and our excellent track record as a poultry processor, and we will remain so. We are doing more than any other business in addressing the key issues our sector is facing and we are leading the way in establishing and enforcing industry best practice.
"The company has an open policy to engage with key stakeholders such as local authorities, the media and government bodies. We have also kept our customers fully informed as soon as we were contacted by The Guardian. We will be working to actively engage further with our stakeholders in the coming weeks in order to reassure them about our operations in the light of this inaccurate and misleading article."
Which? executive director Richard Lloyd said: " The Guardian's investigation raises serious concerns. Tackling campylobacter has to become a much bigger priority for supermarkets and their suppliers as it is responsible for thousands of cases of food poisoning and the deaths of 100 people every year.
"It's therefore disappointing that the FSA has gone back on its commitment to publish in full the quarterly data on the levels of campylobacter in supermarket chickens, when it is clearly in the public interest to do so. The FSA must put consumers first and operate more transparently than this."