Andy Bond, CEO of Wal-Mart's Asda supermarket chain has ordered an internal investigation into why tens of thousands of his employees refuse to shop at the company's stores, according to the Independent on Sunday newspaper.

Bond has told his store managers that nearly 50,000 staff decline to do their weekly shopping with the company and he wants to know why, the paper said.

Asda insists that the true figure is less than half that, but Bond gave the higher estimate in a meeting this summer with managers from most of the group's 281 stores, it said. The chief executive's calculation would mean that two in five employees shop elsewhere, despite a 10% discount on goods.

The news comes on top of the decision by Mr Bond to scrap a special staff discount on toys, DVDs and drinks this Christmas. Instead of the usual 20% price cut, they will get the normal 10%.

Giovanna Holt, a former Asda employee who is now an official of the GMB general union, said the reluctance of "colleagues" - as Asda calls them - to shop at the chain was a symptom of low morale and a sign that they had to shop around to get the best bargains. "Although Asda boasts that its prices are among the lowest, the colleagues' pay is at or near the national minimum wage and they have to buy the cheapest lines in different stores to make their money go further. A lot of them have to live hand to mouth," Holt said.

She said under the "anti-union" Wal-Mart group, the stores chain had attempted to squeeze "more and more" out of the workforce and employees were resisting it. She added that senior managers spoke to "hand-picked" employees only when they visited stores.

A spokesman for Asda said about 22% of employees did not get their weekly shop at Asda, but it was difficult to work out the precise proportion. He "did not recognise" the figure attributed to Mr Bond which would amount to 40% of the workforce.

A spokeswoman for the stores group denied there was a problem with morale or that senior managers spoke to hand-picked employees only. She said regular "listening groups" undertaken by managers at stores showed morale was high and "growing steadily".

She "struggled to understand" the union's allegations, and said no such mood had been picked up in a confidential, online reporting system in which employees were encouraged to be honest about management.