In Maryland, employees work "at the will" of their employers. This means, in the absence of an express contract, agreement or policy to the contrary, an employee may be hired or fired for almost any reason -- whether fair or not -- or for no reason at all.
There are certain exceptions to this general rule which provide some protection to employees from illegal discrimination based on such categories as race, color, gender, national origin, religion, age, disability or marital status.
This is not legal advice nor does it create an attorney-client relationship. This is for education and informational purposes only. It is always recommended that you contact an attorney with any concerns as each individual case is unique.
As a general principle of law, an at-will employee may be fired for any reason or no reason at all, unlawful discrimination and unlawful retaliation excepted. Except where the rule has been changed by statute, such as a statute making it unlawful for an employer to fire an employee for lawful conduct outside the workplace, an employee may be fired for keeping a messy house. It's not fair, and it may not even be rational, but no principle of law protects employees from being terminated for irrational reasons that are otherwise lawful.
Not legal advice as I don't practice law in Maryland. It's just my two cents on the facts you describe in light of general principles of law. If you need legal advice, please consult a lawyer who holds Maryland licensure. I practice in Vermont ONLY.
It is certainly unusual and actually a bit bizarre, but there is nothing actionable on its face if an employer were to terminate someone bc they keep their house messy.
It makes me suspect that something else is going on. There must be some facts left out. Why is a neighbor calling your boss? Why does your boss care what your house looks like?