Can I charge more if someone drops off an animal for boarding with fleas?

Someone dropped off a cat tonight as I was checking him over he has fleas. I told the owners as I was checking him I saw a few (I also had a flea comb right next to him ironically) and they seemed upset due to him getting a flea treatment last week and apologized. I said it was fine but I have four other animals that will now have to get flea treatment baths tomorrow just to be safe and the whole room bleached and sanitized to prevent further infestation. Would it be wrong of them to charge an extra few dollars since I have to do more work cleaning up and preventing my animals getting them or is that rude?