Thank you for the information and your question. I agree with you that, at least on it's face, the rationale for sending you home may not make sense or even be a good management decision. However, unless you have a contract for a specific term that guarantees you a minimum number of hours, or there is a company policy that prohibits this behavior, it is not illegal. In other words, an employer is always free to set and change the terms and conditions of employment, including sending an employee home early from their shift, as long as a contract or policy does not guarantee otherwise.
The only other exception, is that an employee may not be targeted for adverse employment actions, such as a cut in hours, simply because that employee is a member of a protected class under employment discrimination
laws. In that case, if you felt like you were being targeted because you are in a protected class, you would first have to file a discrimination compliant with your employer's HR and then if they couldn't resolve the issue, you could file a complaint with the EEOC
Some states do have laws that guarantee that an employee must be paid for a minimum amount of time when they show up as scheduled, but Maryland is not one of those states. So, theoretically, an employee could be sent home as soon as they came in and not entitled to any pay other than the few minutes they were at work before being told to go home.
Please let me know if you need any clarification. I would be glad to assist you further if I can.