Wal-Mart and Big Labor are perfect enemies. The nonunion retailer’s entire business model is based around keeping costs low, including labor costs. It has been extraordinarily successful too, but unions now think they have found its weak spot: the company’s supply chain.

A major part of Wal-Mart’s success has been its extraordinarily efficient logistical system. It maintains one of the world’s largest private communications networks as well as massive databases on sales and merchandise.