Wal-Mart Stores has defended its relationships with trade unions across its global operations in a bid to calm opposition from workers groups in South Africa to its move to buy a majority stake in retailer Massmart Holdings.

One South African union official said that Wal-Mart has made “relentless attacks on workers and unions“, elsewhere said his to attempts to engage with the US retailer had “thus far been discouraging”.

However, the world’s largest retailer insisted its corporate position was to “honour pre-existing union relationships” and that it was “committed to working constructively with the local unions in South Africa”.

A spokesperson for the Wal-Mart told just-food that approximately half of its international operations have unions at some level and that its UK arm Asda has seen union membership grow and has been “routinely recognised as one of the best employers in the country”.

Earlier today, shareholders in Massmart voted overwhelmingly to support Wal-Mart’s plans to buy a 51% stake in the retailer for around US$2.3bn.