The Trump administration is threatening to punish some immigrants in the U.S. illegally with criminal penalties, including jail time and fines, if they fail to sign up for a government registry.

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.

In one of his 10 inauguration day executive orders related to immigration, President Donald Trump initially outlined plans for creating a registry and required that Homeland Security “immediately announce and publicize information about the legal obligation of all previously unregistered aliens in the United States to comply.”