If you are a U.S. lawful permanent resident (green card holder) who has had a run-in with law enforcement authorities, you are right to be concerned. A record of criminal activity can lead to the loss of one's U.S. permanent resident status and thus deportation from the country—in some cases, regardless of whether you were actually convicted of a crime.
If you are still facing criminal charges, but nothing has been finalized, speak to an immigration attorney immediately—even if you already have a criminal defense attorney or public defender.
Often, defense attorneys know little of how a particular strategy in criminal court will impact your permanent resident status. And in case you're ultimately found guilty, now is the time to make sure that the conviction and sentence will do the least damage to your ability to keep your green card. Sometimes, for example, exactly which crime a person is charged with can make a huge difference in immigration terms, and the prosecutor might be willing to agree to a slight change. Or maybe you could spend a little more time in jail in return for a reduced sentence that would protect your green card.
An immigration lawyer can help you and your defense attorney discuss whether such options are possible, and devise a strategy before the process has gone too far.
The biggest question, if you have been arrested for a crime and been through the criminal court system, is what was the final result? In many instances, whether you can be found deportable depends on whether you were actually "convicted" of a crime. The term "conviction" means, under the immigration laws, that you were both found guilty and had some sort of punishment imposed. Also, in most U.S. court circuits, you were convicted of a crime only if the decision in your case is final, that is, not under appeal.
Being found guilty can include formal findings by a judge or jury, a plea of guilty or nolo contendere, or having admitted sufficient facts to warrant a finding of guilt. Punishment includes a penalty (such as a fine or community service) or a restraint on liberty (such as jail). (See the Immigration and Nationality Act at I.N.A. § 101(a)(48)(A), 8 U.S.C. § 1101(a)(48)(A).)
There are various situations in which you would not be found to have been convicted of a crime. For example, no conviction exists after a juvenile delinquency finding rendered in juvenile court, an acquittal, or a dismissal before conviction or after deferred prosecution or a deferred verdict (assuming that you didn't separately plead guilty or no contest, or admit facts sufficient to justify a conviction). See an immigration attorney for a full analysis.
For a green card holder, indications that you have abused or are addicted to drugs can make you deportable. These are sometimes referred to as "conduct-based" grounds of deportability, because they depend on the U.S. government's assessment of your actions and admissions, not on whether you were convicted of a crime.
An even broader array of crimes can make a person "inadmissible." This is less likely to affect you as someone who already has a green card. It is primarily a concern for people applying for green cards and U.S. visas. However, if you travel outside the United States for 180 days or more, or commit a crime while you're away, your inadmissibility could be a problem if you try to return.
Whether or not you've been convicted of a crime is just the begin of a long and complex analysis of the impact of your arrest on your status as a green card holder. The stakes are high, and U.S. immigration laws give the enforcement authorities plenty of room to argue that even misdemeanors and other relatively low-level crimes should make the green card holder deportable. Get yourself a top-quality immigration lawyer as soon as possible.