Can the mother refuse to let the father see his daughter if he owes back child support ?

If you were never married to the mother and you have not established your parental rights by court order, you have no rights to visitation, only an obligation of support. You say there is no custody agreement made through the courts. If that is right, then yes she can because you have no rights. You can establish them though. The lawyers participating in this website cannot solicit business directly from people that ask questions, but you can call the lawyers and should do so. Most if not all will give you a free consultation to discuss the specifics of your case, as well as your chances of success, potential remedies and cost of representation. You need a lawyer in a case like this. Use the Find a Lawyer tab on and look up local family law attorneys and contact them. Most if not all will give you a free consultation in the beginning.