If you obtained your green card through marriage to a U.S. citizen or permanent resident, getting divorced or having your marriage annulled could pose a problem. The issue is whether a divorce casts doubt on whether the marriage was real in the first place, as opposed to a fraud perpetrated in order to get a green card. As you likely know, U.S. immigration laws make clear that only real, valid marriages qualify an immigrant for U.S. residence.
The good news is that there is nothing in U.S. immigration law saying that once people are divorced or their marriage is annulled, their efforts to get a green card are automatically over. U.S. Citizenship and Immigration services (USCIS) recognizes that even couples who were once in love and committed to each other can have their relationship fall apart.
However, it's true that, since USCIS is always on the lookout for fraudulent marriages, a divorce can cause USCIS to do a second round of scrutiny on your case. How this plays out will depend on what phase of the application process you are at.
If the only application filed in your case so far is a visa petition on Form I-130, filed by the U.S. citizen or lawful permanent resident half of the couple, then even if it was approved, that won't help the immigrant after a divorce. The visa petition simply starts the immigration process, without providing the immigrant any rights to remain in the U.S. or be admitted there. And given that the point of a marriage-based visa is to unite a couple in the United States, it would make no sense to grant it after the couple is no longer a couple.
The same is true if the immigrant has already submitted the application for an immigrant visa or green card, but the case has not proceeded to an interview or been approved. So if your marriage ends in divorce or annulment at this stage, you will not be able to take further steps toward U.S. immigration.
If you have already successfully applied for permanent residence (a green card), USCIS has no reason to take a second look at your application just now, so you need not worry.
But we're talking only about permanent residence here, not conditional residence, as described next. The only people who become permanent residents immediately after applying for a green card are those whose marriages were already two years old or older at the time they were approved for the green card or entered the U.S. with their newly granted immigrant visa.
Also remember that, if and when you later apply for U.S. citizenship, you're giving USCIS a reason to take another close look at your file. Read the entry concerning citizenship, below, concerning this issue.
If you have already applied for your green card and were approved for conditional residence (that is, received a two-year green card, as is given to spouses whose marriage was less than two years old at the date of green-card approval), you'll face some challenges when USCIS next looks at your case.
The next USCIS review normally happens approximately two years after your conditional-residence approval date, after you submit USCIS Form I-751, as required. This form asks USCIS to remove the conditions on your residence and approve you for permanent residence (a status that doesn't expire, though the actual card does).
The usual way of filling out Form I-751 is as a joint petition, signed by both spouses. The joint petition tells USCIS that the marriage is still real and ongoing.
After a divorce or annulment, however, you (the immigrant) will, in order to stay legally in the U.S. based on your marriage, have to submit the petition on your own, asking for a waiver of the joint filing requirement. In order to do this, you will need to provide convincing evidence that the marriage started out as the real thing (was "bona fide"), even though it ended before you wanted it to.
Such evidence might consist of the types of things you've sent USCIS before, such as bank and credit card statements showing accounts held in common, children's birth certificates, copies of mortgage or rental agreements, and so forth. However, you should not duplicate things you have sent to USCIS before. Try to use the most recent documents possible.
Interestingly enough, statements from marriage counselors or therapists can be helpful in this regard. People who are committing marriage fraud don't tend to visit a counselor of therapist to try to save their marriage. They know there's nothing real to save.
Your immigration situation gets more complicated if the divorce isn't yet final when your Form I-751 is due, because technically, no waiver is yet available to you. In this case, you will definitely want to get an attorney's help.
If you apply for U.S. citizenship (to naturalize), USCIS will have another chance to review your immigration file, and your marriage information. If USCIS sees any signs that the marriage that got you the green card was fraudulent (and again, divorce or annulment could be considered such an indication), it will require you to provide documentation proving that your marriage was actually bona fide.
By now, there is probably plenty of such documentation already in your file, so you'll need to look for more recent, but also convincing evidence of your marriage being real.
If you're unable to come up with sufficiently convincing documentation, USCIS can not only deny your U.S. citizenship, but refer you to immigration court proceedings for removal from the United States (deportation).
For a personal analysis of whether your divorce or annulment might affect your immigration status, whether to apply for U.S. citizenship, and help with filling out any applications or waiver requests, consult an experienced immigration attorney.