The Trump administration on Monday moved to end asylum protections for most Central American migrants in a major escalation of the president’s battle to tamp down the number of people crossing the U.S.-Mexico border.

According to a new rule published in the Federal Register, asylum seekers who pass through another country first will be ineligible for asylum at the U.S. southern border. The rule, expected to go into effect on Tuesday, also applies to children who have crossed the border alone.