Generally, when a permanent resident applies for US citizenship, he or she ensures that they meet all eligibility requirements and therefore expect to get a favorable response. If you receive an unfavorable response to your US citizenship application and you wish to file an appeal, you may do so by filing a request for a hearing. You can do this by filing USCIS form N-336 (Request for a Hearing on a Decision in Naturalization Proceedings). You must file this form with the USCIS office which returned the unfavorable decision in your case. It is important to file this if you believe that an error has been made in the application process. If you are simply not eligible for citizenship, you may need to speak with a US immigration attorney instead.