Owner trying to claw back wages

Hoping someone might be able to let me know if this would be worth reaching out to a lawyer. I was out for bowel resection surgery for 5 weeks just recently. I had made my employer aware months in advance that I would be out a minimum of 4 weeks. They never said anything about pay and my insurance is through my wifes place of work. I had discussed with her filing for STD but not even sure that's possible.

Regardless, I was paid while I was out and have been back at work for a few weeks. I recently went through jobs that I receive commission on. The owner then said, "Since we paid you while you were out, the commission is a wash and you will be getting nothing." .

Now I understand their perspective but they handle everything this way, reactionary... Can they do this? Seems very illegal. Thanks in advance for any help or if you could point me in the right direction.