Unveiling a report which shows punishing and dangerous work conditions are common among suppliers in developing countries, the charity Christian Aid is urging British supermarkets to examine the practices of companies they purchase from.
It says an increasing number of products sold in supermarkets - where 85 per cent of food is purchased - are from developing countries.
Launching the campaign yesterday, Clare Short, Labour's overseas aid spokeswomen, urged shoppers to put pressure on supermarkets to consider the sources of their goods.
Investigators who traced a range of own-brand foods back to farms and plantations found many problems, including discrimination, low wages and pesticide abuse.
Michael Taylor, Christian Aid's director, condemned the pay and conditions endured by many of the Third World workers as "unacceptable". He said the average fruit farm worker in South Africa, for example, would take more than 15 centuries to earn the annual salary of Sir Ian MacLaurin, Tesco's chief executive.
"We don't want a boycott of the produce we have highlighted or for the big stores to dump certain suppliers. We want them to work with their suppliers to improve conditions, and we know that some are already taking steps in the right direction."
The charity has developed a Supermarket Charter, calling for a code of conduct for all overseas suppliers with independent monitoring. It argues that consumers want higher ethical standards, so improvements make sound business sense. Christian Aid supporters are being encouraged to lobby supermarket managers with messages on the back of their till receipts.
The new report, The Global Supermarket, marks the launch of "Change the Rules", a four-year campaign to win a fairer deal for poorer countries. It details the pay and conditions of workers in six industries.
It claims asparagus in Peru, for example, is being picked and prepared by workers whose typical daily wage of just over pounds 2 is insufficient to feed a family one meal. Christian Aid found Peruvian asparagus in Asda, Marks & Spencer, Safeway, Sainsbury's and Tesco.
In Brazil, the charity claims children as young as six are working on coffee plantations while the demand for good quality grapes has produced a reliance on pesticides which are bad for workers' health.
It also highlights how prawn production has caused significant social and environmental damage in Thailand, India and Bangladesh, where the siting of farms in mangrove forest areas can threaten the livelihoods of small fishing communities.
The trade sometimes leaves workers without enough food to feed their own families, by diverting land away from growing for local consumption.
However, Christian Aid claims action is clearly possible, with the Co- op and Sainsbury already working on a pilot project to ensure good working practices.
The charity says the top 10 British supermarkets, led by Sainsbury's, Tesco, the Argyll Group (including Safeway and Presto) and Asda, have an annual turnover equal to the income of the world's poorest 35 countries and can afford the changes.Reuse content