By Jonathan Birchall

The four biggest groups representing the US retail and clothing industry are calling on Uzbekistan to end the widespread use of child labour in the harvesting of the country's cotton crop.

The coalition is urging President Islam Karimov to take "decisive and immediate actions to end the use of forced child labour in the cotton fields" in the world's second largest cotton exporter.

The most recent US state department human rights report on Uzbekistan, published in March last year, noted that there was "large-scale compulsory mobilisation of youth and students to help in the fall cotton harvest . . . in most rural areas".

Retailers and clothing companies in the US and the UK - including Tesco, Marks & Spencer, Target and Gap - have already taken measures to exclude Uzbek cotton from their merchandise following repeated reports of Uzbek children picking cotton for minimal payments.

In a letter to be delivered today to the Uzbek ambassador in Washington, the National Retail Federation, the Retail Industry Leaders Association, the American Apparel and Footwear Association and the Association of Importers of Textiles and Apparel, say that use of child labour is "totally unacceptable", and note that retailers have told their suppliers to avoid Uzbek cotton.

Patricia Jurewicz, of the As You Sow Foundation, which co-ordinated the NGO and investor coalition, said the groups' letter "sends a clear message that forcing children to pick cotton must end immediately".

Child labour is banned under Uzbekistan's constitution, and the government has in the past argued that child workers volunteer to help with the harvest.

Uzbekistan produces more than 800,000 tonnes of cotton annually, worth more than £500m. About a third is used in Europe, after being processed elsewhere in Asia.

Three state-owned conglomerates buy harvested cotton at prices fixed by the state, allowing the government to net the difference with the global price for the commodity.

President Karimov's autocratic regime has suppressed political dissent in the country. In 2005, security forces opened fire on protesters in the eastern city of Andijan, killing hundreds of people.