More than a million migrants who were allowed to enter the United States during the Biden administration can have their temporary stays revoked and be rapidly deported, according to an Immigration and Customs Enforcement document that became public Friday.

Those who followed Biden-era guidelines are dismayed that the rules have changed. The app that helped them enter the country now may make them targets.

The U.S. Department of Homeland Security memo provides guidance for the use of a fast-track deportation process that the Trump administration reinstated earlier this week, suggesting officers focus on migrants who failed to request asylum within a one-year deadline after arriving in the U.

The Department of Homeland Security says it is continuing to accept requests for asylum-seekers arriving at the U.S.-Mexico border, and is authorizing travel for certain nationals of Cuba, Haiti, Nicaragua and Venezuela seeking to lawfully enter the United States through a humanitarian parole program beyond Jan.

Many of the migrants under threat spent months waiting in Mexico, at migrant shelters or in rented rooms, in cities that are rife with cartel violence and kidnappings, in order to enter the US with permission.