Moving out of state with my son...what can the dad do?

I have a 5 year old son and am getting married to someone in the military we will have to move of course and I am wondering what my son's father can do to stop me he hasnt seen his son in over a year and has never supported him money wise but some how he got wind of the fact i might be moving and now has been contacting me tell me he has gotten himself a lawyer. i on the other hand can not afford a lawyer so i am looking for some insight on this and if anyone has been in the same situation as me!