I'm an exempt employee. I've already worked 45 hours for the week and I want to leave 2 hours early on Friday. My HR person says they will take 2 hours off my PTO bank to cover the 2 hours I leave early. Can they do this or can they only take my PTO time

HR has taken time out of my PTO bank because I left early one day. As an exempt employee I understand Federal law says I have to be paid for the full day if I only worked a partial day. They say they have the right to take my PTO to cover any time I'm not here during the day until it's exhausted. She says she can take it because I left early during the time we are open for business regardless of how many hours I have already worked for the week. So, I can work 50 hours for the company and if I leave for 2 hour for a doctors appointment, they can dock my PTO bank? Doesn't seem fair!