WASHINGTON, D.C. — President Donald Trump moved to end asylum protections for most Central American migrants who cross the U.S. southern border as he steps up a crackdown on immigration.

Migrants who fail to apply for protection from persecution or torture while in a third country before entering the U.S. would be ineligible for asylum, under a rule set to be published today in the Federal Register by the Trump administration.

“The large number of meritless asylum claims places an extraordinary strain on the nation’s immigration system,” according to the notice. It also said the claims undermine “humanitarian purposes of asylum” and has worsened human smuggling.

Trump has focused on cracking down on undocumented immigration — one of his signature issues — for weeks as his 2020 re-election campaign gets underway. He prodded Mexico to take steps to block migrants from crossing into the U.S. after threatening the country with tariffs on goods last month.

Trump dropped plans for tariffs after a June 7 agreement with Mexico that called for its authorities to take new steps to prevent migrants from crossing into the U.S. Trump has said Mexico has done “an outstanding job.”

The administration said last week that the number of people caught illegally crossing into the U.S. or turned away at the Mexican border dropped to 104,000 in June, compared to 144,000 a month earlier.

Still, it’s not clear how much of the decrease can be attributed to hotter temperatures versus Mexican law enforcement efforts along migration routes. The number of migrants apprehended in June were still more than double the same time a year ago.

The Trump administration said there’s been a sharp increase in migrants claiming fear of persecution or torture when caught by U.S. authorities. The number of cases referred by the Justice Department for proceedings before an immigration judge has more than tripled between 2013 and 2018, according to the Federal Register notice.

“Only a small minority of these individuals, however, are ultimately granted asylum,” according to the notice.