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.

For weeks, lawyers and advocates, worried about President Donald Trump’s promised immigration crackdown, have been telling asylum seekers and migrants temporarily paroled into the United States to keep their documents with them at all times in case they are stopped by overzealous cops or immigration agents.

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.