Asda is set to face increased union pressure after an international union movement stepped-up calls to mobilise Wal-Mart workers around the world.
Union Network International is pressing for more union representation at Wal-Mart stores and improved staff pay.
Asda, the UK subsidiary of the US giant, was highlighted during the UNI annual conference for its staff’s low union membership.
Wal-Mart does not recognise unions in the US but says that staff overseas are free to join a union if they choose.
The retailer’s workers in Germany, Brazil and Argentina have joined unions, but labour organisations claim it has resisted union demands elsewhere and that its general hostility towards unions has deterred union activity.
At its conference in Chicago, UNI said it would launch a concerted global campaign to increase worker representation at Wal-Mart stores.
The UK is set to be one of the countries targeted by UNI along with South Korea, Mexico, and Japan, as well as Brazil, Argentina and Germany.
The action, which could include some stoppages at German stores, is designed to end what the union described as a "downward spiral" in the pay and working conditions of Wal-Mart staff.
Wal-Mart has always maintained that it has no official ban on unions and stressed that it was seen as a model company in many of the countries in which it operated.
A spokesman said: “Our employees can choose whether they want to be union members or not and overwhelmingly they have not.”
With 1.6 million staff, Wal-Mart is one of the largest private sector employers in the world.
