The question you want answered is not, "Is this fair?". Instead, the question you want answered is "Is this legal?"
I know of no law that makes it illegal for an employer to dock the salary of someone when they are out sick. I know of no law that requires an employer to pay employees sick pay. It's *not* fair. But I don't think it's illegal.
I'm not licensed in Texas so don't take that as legal advice. It's simply information based on general principles of law which is intended to educate. If you need legal advice, please consult a lawyer who holds Texas licensure.