WASHINGTON, D.C. — U.S. Citizenship and Immigration Services announced that most immigrants seeking a green card must leave the country and apply at a U.S. embassy or consulate abroad through consular processing. Noncitizens in the United States temporarily, including students, temporary workers and tourists, must return to their home countries to apply, except in extraordinary circumstances.

The agency said adjustment of status will be granted only in extraordinary circumstances on a case-by-case basis. The policy closes a loophole that had allowed visa holders and visitors to apply for a green card while still in the U.S. For more than half a century, foreign nationals with legal status could apply for and complete the entire process for permanent residence while inside the country.

"We're returning to the original intent of the law to ensure aliens navigate our nation's immigration system properly. From now on, an alien who is in the U.S. temporarily and wants a green card must return to their home country to apply, except in extraordinary circumstances," USCIS Spokesman Zach Kahler said in announcing the change. USCIS said the move is consistent with longstanding immigration law and immigration court decisions.

"When aliens apply from their home country, it reduces the need to find and remove those who decide to slip into the shadows and remain in the U.S. illegally after being denied residency. This makes the system fairer and more efficient." Kahler added: "Following the law allows the majority of these cases to be handled by the State Department at U.S. consular offices abroad and frees up limited USCIS resources to focus on processing other cases that fall under its purview, including visas for victims of violent crime and human trafficking, naturalization applications and other priorities."

"Our system is designed for them to leave when their visit is over. Their visit should not function as the first step in the green card process." The Department of Homeland Security said in a statement, "The era of abusing our nation's immigration system is over." The agency said immigration officers are being directed to consider all relevant factors and information on a case-by-case basis when determining whether an alien warrants this extraordinary form of relief.

"This is a largely unprecedented move that will limit lawful immigration to the U.S. greatly. People who followed the rules faithfully now face tremendous uncertainty," former USCIS senior official Michael Valverde said.

According to the Cato Institute's director of immigration studies, more than a million legal immigrants are waiting for approval on their adjustment of status green card applications. Obtaining a green card is a multi-step process that can take months to several years, and being a green card holder allows a person to live and work permanently in the U.S. According to the U.S. State Department, overstaying a U.S. visa can lead to deportation, ineligibility for future visas and re-entry bans lasting up to 10 years. The Trump administration has instated bans or restrictions on citizens from nearly 40 countries, and a separate policy this year paused all visa issuances to immigrant visa applicants from 75 countries.