The move, which could expose unregistered migrants to criminal prosecution, represents a drastic escalation of the administration’s efforts to push millions of immigrants to leave on their own.

The Trump administration is creating a registry for all people who are in the U.S. illegally, and those who don’t self-report could face fines or prosecution.

But lawyers and immigrant advocates warned that the administration’s plan was on shaky legal ground and that some immigrants may be afraid to comply.