Once you become a card holder of Mexico, as in a temporary or permanent resident, you are now obligated to follow specific procedures when it comes to entering and exiting the country. Long gone are the days when you can just walk through customs and board the plane or drive across the border. Now, you have to check in with INM.
Don’t worry, this does not mean you have to go to your nearest INM office and stand in a long line up, nor does it mean you have to have permission to leave Mexico. It simply means that in order to retain your Mexico residency, your comings and goings are recorded differently. This avoids you entering or exiting as a tourist, which if were to happen, would void your current residency and return you back to being a visitor or tourist with a 180-visa.
In accordance with Article 47 of the Immigration Law, foreign nationals living as residents in Mexico must notify INM of their departure at the airport. You are required to show your current passport and Resident Card.
Once there, you will be given the form that needs to be filled out to pass through immigration, however, this form is filled out differently if you are a card-holding resident of Mexico.
The reason you need to notify INM of your departure is because Mexico currently has a system that when a foreign national’s passport is scanned, his/her entries and departures are recorded. The passport’s data is linked to the temporary or permanent resident card information that, in turn, stores the information on entries and departures.
If you want to leave Mexico but forgot your resident card, the best thing to do is cancel your flight and return home for the resident card. Exiting improperly will result in your residency being canceled. Not having your residency card will result in losing your current status or the one pending if you have.
If you left Mexico with your resident card but forgot it abroad, when entering Mexico you need to tell the airport Immigration Officer that you are currently in an irregular migratory situation in the country but wish to normalize your situation and do not want to enter as a tourist.
Be prepared for a fair bit of grief.
They will run your passport to verify that you actually have a resident card. You will then be presented before the Migratory Authority. You may also be taken to a migratory station. If you prefer, you are entitled to have legal counsel with you.
It is possible that you will be held for a few minutes or a few hours, after which time the INM officer will likely give you an official document that will require you to appear at an INM office to apply for a normalization process.
In the event of a favorable normalization process, the National Migration Institute will issue a new resident card with the migratory condition you held and next time, remember your card.
You can review the immigration law here: https//www.juridicas.unam.mx/legislacion/ordenamiento-ley-de-migracion