Multiple hours taken off my vacation hours for requesting time away on days i was not on schedule

I was not even scheduled and requested the time off well in advance just in case i would be. A weekend of 3 days was requested, while I usually was scheduled for only Saturday evenings. The manager kept pushing me to say the whole weekend. I don't know if this was legally allowed. Instead of the 8 hours for Saturday, the manager put 3 whole days of work for my leave, 3 whole days of vacay.