Here's an article:
Baltimore Business Journal
Remember "company scrip", the currency issued in certain industries to pay workers. Such scrip can only be exchanged by wage-earners in company stores owned by their employers and often charging inflated prices. In the UK, such systems have been formally outlawed under Truck Acts.
In the U.S., mining and logging camps were typically created, owned and operated by a single company. These remote locations were cash poor and workers had very little choice but to purchase goods at a company store. With this economic monopoly, the employer could place enormous markups on goods, making workers completely dependent on the company, thus enforcing employee loyalty.