Question about being called in on my day off

So I was supposed to be off today, Black Friday. PM messaged me last night that he needed me to come in today. I never responded until this morning when he told me I’d be considered AWOL since he messaged me yesterday. Could I be fired for not showing up? I’m way past my 90 days. I’ve been working there almost 2 years now. But I’d like to know the actual rules on this matter. I’m a rural carrier