Eagle Corp recently gave out bonuses to all of its employees to celebrate the hard work put into getting their new product to the market in record time. Three departments (i.e., Shipping, Production, and Quality) worked mandatory weekends for 2 months in order to accomplish this goal. However, the employees in the Shipping, Production, and Quality departments are now upset and unmotivated because other departments (like Accounts Payable) received the same bonus without having to work mandatory overtime. This case is an example of which theory?

Herzberg's two-factor theory

Reinforcement theory

Expectancy theory

Equity theory