The GMB union has sent a letter to 62 employment agencies warning them that they could break the law if they supply staff to Asda.

The union is currently in a long-running dispute with Asda over working conditions and union recognition, and a ballot on possible strike action at 20 Asda distribution centres closes tomorrow.

The GMB claims that employment agencies are pre-loading staff into depots to break the strike if GMB members vote for strike action.

Jude Brimble, from the GMB, said: “This pre-loading is illegal and Asda is trying to lure employment agencies into the dispute by this tactic.”