The Permanent Resident Card (Green Card) is for living permanently in the United States. If after getting the green card, you want to live for more than six months outside the United States, there is a presumption that you do not want to live permanently in the United States, and therefore have abandoned your Permanent Residency Status.
In order to preserve your Permanent Residency status, you need to file the Reentry Permit (Form I-131) BEFORE you leave the United States. After filing you have to have a fingerprinting done, so it’s advisable to file at least 1-2 months prior to departure. Also please include a valid reason in the cover letter as to why you are leaving. The reentry Permit can be mailed to you or be picked up at the US Consulate near the foreign country that you are in. Please note that if you have committed a crime or are otherwise excludable from the United States, you cannot use the reentry permit to enter the US.
The Reentry Permit is usually valid for 2 years, before which time you have to come back to the United States. Of course you can come back and file the reentry permit again, for another two years, but you have to have a valid excuse. Usually it is not a problem if an US business transfers you to their foreign location, or if you leave to study under any particular program of study in another country. However if you are just working for a foreign company in their office in your home country, you probably will not get the reentry permit and have to forfeit your green card.
Please also bear in mind that using the Reentry Permit may not prolong your continuous residency requirements for your citizenship. Therefore getting the citizenship will be delayed beyond the normal times.
Contact Houston Immigration Lawyer, Annie Banerjee for more details