While this schedule change is unfortunate it is not illegal. The fact is that most work relationships are what is known as "at will". This means that an employer has the right to change the terms and conditions of the workplace much as it sees fit. This includes last minute changes to an employee's schedule.The above holds true absent company policy or the the terms of an employment contract or union agreement to the contrary. Also, your treatment must not have been due to any form of actionable discrimination. Otherwise, I'm afraid that you must work the days that you have been scheduled for.