President Trump on Friday set a cap for the U.S. to accept just 18,000 refugees this fiscal year, marking the lowest number since the modern refugee system was created nearly 40 years ago.

The president also announced major changes to the way the refugee program runs, creating a set-aside of 5,000 slots for refugees fleeing religious persecution, 4,000 for Iraqis and 1,500 for key Central American partner countries. Those all count against the 18,000 cap.

The number, which the administration had signaled in late September but was made official by Trump’s determination, has been criticized by both Republicans and Democrats on Capitol Hill, who said the U.S. has an obligation to accept more refugees.

Administration officials, though, argue that the U.S. already has a massive asylum backlog that it needs to work through. Refugees are those who are awarded humanitarian protections while they are outside the U.S. Asylees are those who make it to U.S. soil and then request protection from their home countries.

But Homeland Security officials say the same adjudicators work both types of cases, and they have been overwhelmed by the surge of asylum-seekers at the border, so cutting the number of refugee cases is justified in order to give the officers a chance to eat into the backlog.

“The admission of up to 18,000 refugees to the United States during Fiscal Year 2020 is justified by humanitarian concerns or is otherwise in the national interest,” Mr. Trump said in announcing the new number.

At 18,000, the cap is 12,000 lower than Mr. Trump set for fiscal year 2019, and it’s a major reduction from the 110,000 refugee target the Obama administration tried to set for 2017.

Mr. Trump in September issued an executive order giving localities a chance to consent before refugees are sent to their jurisdictions.

It’s an issue a number of jurisdictions raised several years back when the Obama administration was inviting refugees from the war-torn terrorism hotbed of Syria, raising security concerns in some areas of the U.S.