If you are being petitioned (sponsored) to immigrate to the U.S. by a family member or U.S. company or employer, and your visa category is one in which the law places annual limits on how many visas can be given out in total, high demand might create a situation where you must wait years to obtain an immigrant visa and green card. It's a first-come, first-served system. That makes it even more surprising that the waiting list you are on might not always move forward smoothly, but instead can stall or even reverse course.
We'll explain the reversals here, the technical term for which is "visa retrogression."
Although some categories of would-be immigrants to the U.S. are eligible for an immigrant visa or green card as soon as their application is submitted and processed (most notably, immediate relatives of U.S. citizens), many other people only fit into categories within the "preference" system. They are subject to annual limits on "visa numbers," and the numbers often run out over the course of the government's fiscal year.
The more people start the application process to immigrate to the U.S. in the various preference categories, the longer the waiting list gets. In some categories, the wait tends to be a modest two to five years, while in others (most notably for siblings of U.S. citizens) it's typically over 20 years. See Green Card Qualification for a list of categories of preference relatives and employees.
As explained in How Long Is the Wait for Your Priority Date to Become Current?, your place on the waiting list depends on your "priority date." That's either the date that U.S. Citizenship and Immigration Services (USCIS) received the I-130 petition that your family member filed for you or the date the U.S. Department of Labor received the labor certification ("PERM") application that your employer filed for you.
For example, let's say Manuel, an unmarried 24-year old from Mexico, has a U.S. lawful permanent resident father who filed a Form I-130 petition for him on February 1, 2023. USCIS approves the petition, thus making February 1, 2023 Manuel's Priority Date. The first thing Manuel does next is to check the State Department's Visa Bulletin, a list showing "cutoff dates," or which Priority Dates are "current," meaning that their holders are now entitled to visas.
If Manuel had checked the Bulletin for February of 2023, the cutoff date he would have seen in his category (F2B) was "01JUN01," or June 15, 2001. That would have told him that people whose I-130 petitions were submitted around 22 years before his were only then receiving visas (green cards), and he could expect to wait around the same length of time.
As the months and years go by, and Manuel regularly checks the State Department's monthly Visa Bulletin, he sees the cutoff dates getting closer and closer to his Priority Date. Only when he sees a date that's at least one day later than his, however, can Manual proceed with his green card application, assuming he is still unmarried. (Priority Dates often move forward by seven days at a time.)
At that point, if Manuel were living overseas, he could expect to get notification from the U.S. National Visa Center (NVC) to proceed with processing for an immigrant visa through a U.S. consulate in Mexico. Or, if living in the U.S. lawfully (or otherwise eligible to use the procedure called "Adjustment of Status"), he could go ahead and mail the required paperwork to USCIS, and await a green card interview.
The above example describes the way the visa/green card application process normally works for people in the preference categories. But sometimes, so many people apply after a certain Priority Date is published that the State Department gets overwhelmed, and needs to put on the brakes. It does this by moving the Priority Date in that particular visa category backward. The case can go nowhere until the Priority Date moves forward again; the government will put it on hold. Fortunately, this situation should not last long.
If your Priority Date is current this month, but you see in the Visa Bulletin that it's due to go backward to a Priority Date before yours next month, you might, if you are in the United States legally, be able to move forward with your application nonetheless. If you are eligible to use the U.S.-based procedure known as adjustment of status, you can try to do everything possible to submit your adjustment application this month.
If you don't, you'll be back to watching the Visa Bulletin each month to see when your next window of opportunity opens up.
Even though the cutoff date for your category will retrogress next month, your adjustment application will remain pending. USCIS will simply wait until your priority date again is current before it moves ahead on or approves your application.
An experienced attorney will have plenty of experience dealing with the odd progress of priority dates, and can assist with the task of keeping your case on track.