For those that have U.S. Permanent Residency (Green Card Holders) but are planning on leaving the United States for an extended period of time (over a six-month period), one should file for the I-131 Re-Entry permit. Those that have not filed and have been absent from the United States for a long duration, can risk having their Green Cards confiscated, or can be made to “give up” their Green Cards while attempting to re-enter the U.S. as they have “abandoned” their Legal Permanent Resident (LPR) status. How to apply for a US Re-Entry Permit
In order to apply for the I-131, one has to be physically within the U.S. when applying and should have a valid reason for leaving the U.S. Further, one should continue to maintain strong ties to the U.S. (which can come in a variety of different forms) as even with the I-131, there have been cases that an over-zealous officer has attempted to make the LPR give up their status. Cases such as these can be rectified slightly easier because of the I-131 but unfortunately, there are no guarantees.