U.S. authorities will examine the social media of foreigners seeking to enter the country as the Trump administration seeks to bar people it believes have engaged in antisemitic activity, the Department of Homeland Security announced Wednesday.

DHS said it would seek to keep out people who have demonstrated “support” for what it called “violent antisemitic ideologies” and organizations such as Hamas, Palestinian Islamic Jihad, Hezbollah, or the Houthis.

The announcement raised immediate concerns, including how the U.S. would define what constitutes the support of antisemitic activity and whether any criticism of Israel or its conduct of the war in Gaza would be enough to bar someone from the country. It also raised broader questions about free speech and civil liberties.