I work at a blue collar place where it is fairly common for employees to change departments, and different department have different hourly pay rates.
A coworker of mine changed departments in order to get better hours and was asked to help out in his old department because they were crazy behind and short staffed and his new department has been slow lately. He agreed. However his old department payed more than his new position, over $1/hour more.
He worked one week in his old department. When his paycheck came, he noticed that he was never payed the difference for working in another department. He took this issue to HR and they told him that since his titled position was that of another department, he was only paid his normal rate. They were shorting him roughly $50.
He agreed to do the company a favor and in return they shorted him roughly $50. It’s not a lot, but it’s the principle. He was eventually paid the money, but only because our manager stormed in to HR and demanded they correct the situation