For the protection of the United States, people with histories of criminal or terrorist activities, drug abuse, infectious medical problems, or certain other characteristics will never be allowed a visa, green card, or U.S. entry. In immigration law terms, these characteristics are known as the grounds of inadmissibility. Following is a short, summary list of the major categories of inadmissibility. It includes a description of whether there's a chance of applying for an official waiver, which forgives or overlooks the inadmissibility problem in your case.
Major Grounds of Inadmissibility
|Classes of Inadmissibility||Waivers Available?|
|People with communicable diseases like tuberculosis
People with physical or mental disorders that
|Drug abusers or addicts||No|
|People without proper vaccinations||Yes|
|People with convictions for crimes involving moral turpitude||Yes|
|People who have violated immigration laws||Yes|
|People with multiple criminal convictions||Yes|
|People likely to become dependent on
need-based government assistance
Everyone who applies to enter or stay in the United States, no matter how long the person plans to be here or whether the person already has a green card, is checked to see whether he or she is inadmissible.
For details on immigration violations that can make you inadmissible, see "Consequences of Unlawful Presence in the U.S.: Three- and Ten-Year Time Bars," and "The Permanent Bar to Immigration for Certain Repeat Violators." For details on criminal violations that can make you inadmissible, see "Crimes That Make U.S. Visa or Green Card Applicants Inadmissible." Also see "Terrorism and Other Security Violations That Make U.S. Visa or Green Card Applicants Inadmissible."
What Happens If You're Found Inadmissible
The various agencies handling your immigration-related applications may decide you are inadmissible any time you ask for permission to enter or stay in the United States. These agencies include the U.S. State Department and the Department of Homeland Security, through its subagencies Customs and Border Protection (CBP) and U.S. Citizenship and Immigration Services (USCIS, formerly the Immigration and Naturalization Service, or INS).
These agencies can use your inadmissibility to block you any time you try to cross the border, apply for a green card, or apply for any other type of visa or immigration status. If you're at a U.S. border when this occurs, you will be turned around and sent home. If you're in the United States, you will, if you have no other visa or status, be sent to immigration court for removal from the United States.
Even a permanent resident (green card holder) isn't safe from being found inadmissible. If a permanent resident departs the United States for more than 180 days, it's possible for him or her to be found inadmissible upon return. This situation might arise, for example, if the person had committed a crime, had developed tuberculosis, or had begun receiving public assistance since receiving the green card.
If you hold a green card, one way to avoid this problem is to apply for U.S. citizenship as soon as you're eligible. For more information on applying for citizenship, see Becoming a U.S. Citizen: A Guide to the Law, Exam, and Interview, by Ilona Bray (Nolo).
Overcoming a Finding of Inadmissibility
Even if you fall into one of the categories of inadmissibility, you may not be absolutely barred from getting a green card or otherwise entering the United States. You may be able to get around the problem, for example if your illness can be cured or the doctor diagnosed you wrong, or the U.S. government made a mistake in your case and you aren't really inadmissible. If all of these fail, you may be able to apply for a waiver, meaning you ask the U.S. immigration authorities to overlook the problem and admit you anyway.
There are many technical factors that control whether you can overcome a finding of inadmissibility. For more on the grounds of inadmissibility and how to overcome them, see the book U.S. Immigration Made Easy, by Ilona Bray (Nolo). Or if you're applying for a green card, get a quick overview of the possibilities in the article, "When Is a Waiver of Inadmissibility Available to a Green Card Applicant?".
You may ultimately need to hire a good immigration lawyer -- see Nolo's Lawyer Directory to find one in your geographical area with experience in this topic area.