Grow Your Business Through Superior Customer Experiences [the broken link was removed] by D. Randall Brandt and Rodger Stotz:

In that study, Oakley found that there is a direct link between employee satisfaction and customer satisfaction, and between customer satisfaction and improved financial performance. Employee satisfaction is a key antecedent to employee engagement. He also found that organizations with engaged employees have customers who use their products more, and increased customer usage leads to higher levels of customer satisfaction.

Managing organizations is a complex endeavor. Employee satisfaction is one factor in an interdependent system that a manager must consider. The challenge is managing the interactions. Most decisions will impact many different facets of the organization. How you weigh the competing desires for profit, pleasing customers, providing good jobs for employees, etc. is what management is about.

This is not a zero-sum game. Good managers grow the pie so all the stakeholders can get more benefit (customers, investors, employees…).