Employer Wants To Take Wages From Employee As “punishment”

Hello!! If you saw my last post, yes it’s the same employer unfortunately ????

I’m technically asking this for a coworker who does not have a Reddit account, but would like some advice on this issue.

For some backstory: She works as a pet groomer in NY and her paycheck is based on commission. Back in January, a dog she was grooming got injured - I won’t go into detail, but it was an INCREDIBLY minor injury and it was absolutely not due to negligence on her part, I was there and can vouch for this. At the time when she asked the salon owner about it - he told her not to worry about it and that she would not be punished for it because it was a mistake, and “this is what we have insurance for”.

A little while ago - I wanna say maybe a week ago - he came into the salon and told her, in front of me and another coworker, that he was going to be taking the commission from her paycheck to refund the woman (she has still not come in for her refund, it’s been a little over a month now). He very specifically told her this was to “punish” her because there had to be “consequences for her negligence”. He also informed us he did not watch the tape from the cameras of the incident, and said he was taking the money from her because he’d “already paid $2,000 to keep us out of the news”. There is no employee contract we can find that says he can do this, no signed agreements or anything.

Her questions are: Is this legal? If this isn’t legal, would someone be able to provide a source for the law in question to help us prove this is illegal?

She currently is not looking to take legal action, because she is very afraid of losing her job - but she would like some proof that this is illegal to have on hand.

Edit: She wanted me to add that because this happened six weeks ago - she has already been paid for this groom. The commission has already been given to her, and he would be taking commission from a completely different paycheck.

Edit 2: For clarities sake - no refund has been processed yet. The woman paid in cash, she would have to physically come into the salon to receive the refund and she has not done so. She was supposed to come in 2 different times before. The first time she got Norovirus, she called us 2-3 weeks later about it, she was supposed to come in a second time but we had a blizzard. This is now the third time she’s supposed to come in. My coworker has already received the commission from this groom like, 2-3 paychecks ago. He would be taking commission out of a more recent paycheck. I will not be going into further detail on the incident due to the erratic behavior of the client. I don’t know if she has a Reddit account, and I do not want to take the risk of her finding out about this and lashing out.