By Jonathan Birchall in New York

Wal-Mart, the world’s largest retailer, said on Tuesday it was asking its suppliers to stop using cotton from Uzbekistan, joining a boycott by global brands over its use of forced child labour during the cotton harvest.

It is the first time the retailer has taken such sweeping action over sourcing issues, reflecting its push over the past three years to improve its record on social and environmental sustainability under Lee Scott, its chief executive.

Wal-Mart played a leading role earlier this year in forming a coalition representing major US retailers and cotton importers which called on the Uzbek government in August to take verifiable steps to end the use of child labour to pick cotton.

In September, the Uzbek government issued a “national action plan” which laid out steps to eradicate the use of children younger than 15 in the cotton harvest. However, it did not involve independent or external mechanisms for ensuring its implementation.

Wal-Mart said that if the steps in the action plan were independently verified, it would lift its decision to avoid Uzbek cotton.

The retailer’s move, which follows similar steps by retailers in Europe, was welcomed by a coalition of ethical investment groups that have been campaigning for US companies to apply pressure to Uzbekistan.

David Schilling, of the Interfaith Center for Corporate Responsibility, welcomed what he called the retailer’s “positive role in crafting a common strategy... to end this egregious violation of children’s rights”.

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”.

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