Chinese law makes it compulsory for any company or institution with 25 or more staff to set up its own trade union if staff request one.
 
The first Wal-Mart trade union in China was set up in mid-2006 and a union office recently opened at the company's HQ.
 
None of Wal-Mart's stores in the US has a union.
 
Wal-Mart, which is the world's largest retailer, opened its first Chinese store in 1996 and now employs more than 35,000 people in its China operations.
 
In March this year, it announced plans hire an additional 150,000 staff as part of a major expansion.
 
Wal-Mart has opened more than 60 stores in 34 cities across China and plans to open dozens more as it seeks to tap China's fast-growing retail market.