If US Customs and Border Protection refuse a green card holder to?
First, if the immigration officer tries to pressure you to sign Form I-407 to surrender your green card, dont do it. Signing it is voluntary and if you voluntarily give up your permanent residency by signing the form, you give up any chance of arguing to keep your green card. US permanent residents (green card holders) are not subject to expedited removal. So if you do not voluntarily give up your green card, and the immigration officer thinks you are inadmissible, they must give you a Notice to Appear in regular removal proceedings in immigration court. You will probably be temporarily let into the US in the meantime while waiting for the immigration court hearing, although theoretically they could also detain you. At the immigration court, you will have the chance to argue to the immigration judge that you are not inadmissible. Think of this as basically an appeal of the immigration officers decision. You can hire an immigration lawyer to appear with you at the hearing if you like. If the immigration judge agrees with you, the removal proceedings will be cancelled, and you will be admitted as a permanent resident again.