The US has introduced a major change to its immigration system, requiring most immigrants applying for green cards to do so from outside the country, marking a significant shift in how permanent residency applications are processed.

Here are five key things to know about the new policy:

1. Most applicants must apply from outside the US

Under the new rule announced by US Citizenship and Immigration Services (USCIS), immigrants seeking a green card will generally be required to leave the United States and complete their application through a US embassy or consulate abroad.

Only in “extraordinary circumstances” will applicants be allowed to complete the process while remaining in the country.