Homeland Security Secretary Kirstjen Nielsen said Thursday that migrants who try to enter the United States illegally will be returned to Mexico for the duration of their immigration proceedings, and won't wait inside the U.S.

DHS and the Mexican foreign ministry simultaneously made the announcement Thursday as Nielsen was testifying before the House Judiciary Committee, where she outlined the plan to lawmakers.

The two countries are calling the policy “Migration Protection Protocols.” A senior administration official described the new policy as “one of the most significant border security developments in decades” on a call with reporters Thursday morning.

“Aliens trying to game the system to get into our country illegally will no longer be able to disappear into the United States, where many skip their court dates. Instead, they will wait for an immigration court decision while they are in Mexico. ‘Catch and release’ will be replaced with ‘catch and return,’” Nielsen said in a statement.

Mexico’s foreign ministry said Thursday that the new policy “will authorize, for humanitarian reasons and temporarily, the entry of certain foreign persons from the United States who have entered the country through a port of entry or who have been apprehended between ports of entry, have been interviewed by the authorities of migratory control of that country, and have received a summons to appear before an immigration judge.”

The move echoes a similar decision DHS made recently to hold migrants outside the U.S. if they try to seek asylum through an official border checkpoint. The new move seems aimed at also holding would-be illegal immigrants in Mexico when they try to enter outside checkpoints.

Nielsen said the placing of illegal immigrants souht of the border will work will reduce illegal immigration because it is “removing one of the key incentives that encourages people from taking the dangerous journey to the United States in the first place.”

DHS noted in a press release announcing the decision that illegal immigrants have “exploited asylum loopholes at an alarming rate.”

Currently, the U.S. has an asylum case backlog of more than 786,000 pending cases.

On Wednesday, a federal judge in the District of Columbia struck down most of the Justice Department’s policy that made it more difficult for immigrants fleeing domestic violence or gang violence to qualify for asylum. U.S. District Judge Emmet Sullivan of the U.S. District Court for the District of Columbia ruled the policies, implemented by former Attorney General Jeff Sessions, violated federal immigration law.

Sessions, who was forced out as attorney general last month, released guidance in June barring immigrants who seek refuge in the U.S. from domestic violence or gang violence from qualifying for asylum.