The Trump administration said Thursday that it is reviewing more than 55 million people who have valid U.S. visas for any violations that could lead to deportation, marking a growing crackdown on foreigners who are permitted to be in the United States.

In a written answer to a question from The Associated Press, the State Department said all U.S. visa holders, which can include tourists from many countries, are subject to “continuous vetting,” with an eye toward any indication that they could be ineligible for permission to enter or stay in the United States.

Should such information be found, the visa will be revoked, and if the visa holder is in the United States, he or she would be subject to deportation.

Since President Donald Trump took office, his administration has focused on deporting migrants illegally in the United States as well as holders of student and visitor exchange visas. The State Department’s new language suggests that the continual vetting process, which officials acknowledge is time-consuming, is far more widespread and could mean even those approved to be in the U.S. could abruptly see those permissions revoked.

The department said it was looking for indicators of ineligibility, including people staying past the authorized timeframe outlined in a visa, criminal activity, threats to public safety, engaging in any form of terrorist activity or providing support to a terrorist organization.