Work says I can't take 12 weeks FMLA

I've called HR and my company will cover for 12 weeks. I'm am part of management, but my boss says I can't take 12 weeks. Is that true? I've tried looking it up online and I have gotten no clear answer. Why would my company say 12 weeks if I can't take it? I'm 15 weeks pregnant, due end of December, and I'm trying to get everything set. I'm not sure what to do, I really wanted to take the full 12 weeks but my boss is saying just 6 weeks. Non of it is payed which I'm okay with.