Colleagues urged to join
Asda has come under pressure from international union UNI, which is stepping up calls for unionisation at parent company Wal-Mart.

According to The Times, UNI director of commerce Jan Furstenborg has also been in talks with Usdaw and the GMB to recruit more members at the UK retailer.

Asda maintains union membership is low, at about 10 per cent, and that it has always respected employees' right to join a union if they wish.

An Asda spokesman said: 'The open and direct dialogue we have with our colleagues is part of the reason why we have been consistently voted as one of the best places to work by them. We won that accolade after we became part of Wal-Mart.'

However, talks broke down at the retailer's Tyne & Wear distribution centre in June, when GMB union members went on strike for a week over pay. At the time, a GMB spokesman accused the retailer of tying pay in with de-unionisation.