I am a LPN, work at long care facility. I'm going to be taking a weekend off,which is my weekend to work.?

Ihave found my own replacement and will be out of state. According to my employer this has been approved, except that if I want to have anyone work for me, I am expected to come in if the replacement calls in. I will also recieve a write up if I don't come in. Does that count as being on-call, or can they do that? Is there a web site I check on.