China has a huge pool of workers, many poorly paid

The purpose of the visit is to give the union an opportunity to see how Chinese bosses treat their workers.

The invitation was extended by Chinese vice-premier Wu Yi during her visit to the US last month.

It came in response to claims by AFL-CIO that China keeps labour costs down by violating workers' rights.

The union earlier this year said China's artificially low wage levels had lured away hundreds of thousands of US manufacturing jobs, and called on Washington to respond with economic sanctions.

Wage pressure

China dismissed AFL-CIO's claims as "completely groundless".

Francis Markus, the BBC's correspondent in Shanghai, says conditions for Chinese workers, especially migrant labourers seeking work in the big coastal cities, are tough.

With a vast pool of rural workers, and in the absence of independent trade unions, employers have the upper hand.

However, some Chinese employers, particularly in the technology sector, are starting to find hey have to offer better pay and benefits in order to retain skilled staff.

AFL-CIO has asked Beijing for assurances that its delegation to China will be free to draw up its own itinerary, and will be allowed to bring its own interpreters.