A worker must be paid for all hours worked, however they have no right to recieve compensation for their time off, even if it is mandated by their employer. That is unless they have PTO to cover their absence or the terms of a union agreement or employment contract provides otherwise. The fact is that most work is "at will", which means that a company can set the conditions of the workplace much as it sees fit. This includes when and why to send an employee home and whether or not to pay them for their time off.